Revert "[base] Replace base::Optional with Abseil"

This reverts commit f2e25f8a.

Reason for revert: Breaks GCC 8.4.0 compilation, see bug.

Original change's description:
> [base] Replace base::Optional with Abseil
>
> Change base::Optional to an alias of absl::optional. Eventually we
> should remove it entirely.
>
> Bug: v8:11006
> Change-Id: I687d44cc7e7cd0a49a84bcc207231eb6808eef2d
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2476318
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#76913}

Bug: v8:11006, v8:12252
Change-Id: I8048dee676a36551d15f25a31d1e171dae00d975
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3173672
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#76976}

BUILD.gn

@@ -4904,8 +4904,6 @@ v8_component("v8_libbase") {
 
   deps = [ ":v8_config_headers" ]
 
-  public_deps = [ ":v8_abseil" ]
-
   data = []
 
   data_deps = []

src/base/optional.h

-// Copyright 2017 the V8 project authors. All rights reserved.
+// Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// This file is a clone of "base/optional.h" in chromium.
+// Keep in sync, especially when fixing bugs.
+// Copyright 2017 the V8 project authors. All rights reserved.
+
 #ifndef V8_BASE_OPTIONAL_H_
 #define V8_BASE_OPTIONAL_H_
 
-#include "absl/types/optional.h"
+#include <type_traits>
+#include <utility>
+
+#include "src/base/logging.h"
 
 namespace v8 {
 namespace base {
 
-using absl::bad_optional_access;
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/in_place_t
+struct in_place_t {};
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/nullopt_t
+struct nullopt_t {
+  constexpr explicit nullopt_t(int) {}
+};
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/in_place
+constexpr in_place_t in_place = {};
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/nullopt
+constexpr nullopt_t nullopt(0);
+
+// Forward declaration, which is referred by following helpers.
+template <typename T>
+class Optional;
+
+namespace internal {
+
+template <typename T, bool = std::is_trivially_destructible<T>::value>
+struct OptionalStorageBase {
+  // Initializing |empty_| here instead of using default member initializing
+  // to avoid errors in g++ 4.8.
+  constexpr OptionalStorageBase() : empty_('\0') {}
+
+  template <class... Args>
+  constexpr explicit OptionalStorageBase(in_place_t, Args&&... args)
+      : is_populated_(true), value_(std::forward<Args>(args)...) {}
+
+  // When T is not trivially destructible we must call its
+  // destructor before deallocating its memory.
+  // Note that this hides the (implicitly declared) move constructor, which
+  // would be used for constexpr move constructor in OptionalStorage<T>.
+  // It is needed iff T is trivially move constructible. However, the current
+  // is_trivially_{copy,move}_constructible implementation requires
+  // is_trivially_destructible (which looks a bug, cf:
+  // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51452 and
+  // http://cplusplus.github.io/LWG/lwg-active.html#2116), so it is not
+  // necessary for this case at the moment. Please see also the destructor
+  // comment in "is_trivially_destructible = true" specialization below.
+  ~OptionalStorageBase() {
+    if (is_populated_) value_.~T();
+  }
+
+  template <class... Args>
+  void Init(Args&&... args) {
+    DCHECK(!is_populated_);
+    ::new (&value_) T(std::forward<Args>(args)...);
+    is_populated_ = true;
+  }
+
+  bool is_populated_ = false;
+  union {
+    // |empty_| exists so that the union will always be initialized, even when
+    // it doesn't contain a value. Union members must be initialized for the
+    // constructor to be 'constexpr'.
+    char empty_;
+    T value_;
+  };
+};
+
+template <typename T>
+struct OptionalStorageBase<T, true /* trivially destructible */> {
+  // Initializing |empty_| here instead of using default member initializing
+  // to avoid errors in g++ 4.8.
+  constexpr OptionalStorageBase() : empty_('\0') {}
+
+  template <class... Args>
+  constexpr explicit OptionalStorageBase(in_place_t, Args&&... args)
+      : is_populated_(true), value_(std::forward<Args>(args)...) {}
+
+  // When T is trivially destructible (i.e. its destructor does nothing) there
+  // is no need to call it. Implicitly defined destructor is trivial, because
+  // both members (bool and union containing only variants which are trivially
+  // destructible) are trivially destructible.
+  // Explicitly-defaulted destructor is also trivial, but do not use it here,
+  // because it hides the implicit move constructor. It is needed to implement
+  // constexpr move constructor in OptionalStorage iff T is trivially move
+  // constructible. Note that, if T is trivially move constructible, the move
+  // constructor of OptionalStorageBase<T> is also implicitly defined and it is
+  // trivially move constructor. If T is not trivially move constructible,
+  // "not declaring move constructor without destructor declaration" here means
+  // "delete move constructor", which works because any move constructor of
+  // OptionalStorage will not refer to it in that case.
+
+  template <class... Args>
+  void Init(Args&&... args) {
+    DCHECK(!is_populated_);
+    ::new (&value_) T(std::forward<Args>(args)...);
+    is_populated_ = true;
+  }
+
+  bool is_populated_ = false;
+  union {
+    // |empty_| exists so that the union will always be initialized, even when
+    // it doesn't contain a value. Union members must be initialized for the
+    // constructor to be 'constexpr'.
+    char empty_;
+    T value_;
+  };
+};
+
+// Implement conditional constexpr copy and move constructors. These are
+// constexpr if is_trivially_{copy,move}_constructible<T>::value is true
+// respectively. If each is true, the corresponding constructor is defined as
+// "= default;", which generates a constexpr constructor (In this case,
+// the condition of constexpr-ness is satisfied because the base class also has
+// compiler generated constexpr {copy,move} constructors). Note that
+// placement-new is prohibited in constexpr.
+template <typename T, bool = std::is_trivially_copy_constructible<T>::value,
+          bool = std::is_trivially_move_constructible<T>::value>
+struct OptionalStorage : OptionalStorageBase<T> {
+  // This is no trivially {copy,move} constructible case. Other cases are
+  // defined below as specializations.
+
+  // Accessing the members of template base class requires explicit
+  // declaration.
+  using OptionalStorageBase<T>::is_populated_;
+  using OptionalStorageBase<T>::value_;
+  using OptionalStorageBase<T>::Init;
+
+  // Inherit constructors (specifically, the in_place constructor).
+  using OptionalStorageBase<T>::OptionalStorageBase;
+
+  // User defined constructor deletes the default constructor.
+  // Define it explicitly.
+  OptionalStorage() = default;
+
+  OptionalStorage(const OptionalStorage& other) V8_NOEXCEPT {
+    if (other.is_populated_) Init(other.value_);
+  }
+
+  OptionalStorage(OptionalStorage&& other) V8_NOEXCEPT {
+    if (other.is_populated_) Init(std::move(other.value_));
+  }
+};
+
+template <typename T>
+struct OptionalStorage<T, true /* trivially copy constructible */,
+                       false /* trivially move constructible */>
+    : OptionalStorageBase<T> {
+  using OptionalStorageBase<T>::is_populated_;
+  using OptionalStorageBase<T>::value_;
+  using OptionalStorageBase<T>::Init;
+  using OptionalStorageBase<T>::OptionalStorageBase;
+
+  OptionalStorage() = default;
+  OptionalStorage(const OptionalStorage& other) V8_NOEXCEPT = default;
+
+  OptionalStorage(OptionalStorage&& other) V8_NOEXCEPT {
+    if (other.is_populated_) Init(std::move(other.value_));
+  }
+};
+
+template <typename T>
+struct OptionalStorage<T, false /* trivially copy constructible */,
+                       true /* trivially move constructible */>
+    : OptionalStorageBase<T> {
+  using OptionalStorageBase<T>::is_populated_;
+  using OptionalStorageBase<T>::value_;
+  using OptionalStorageBase<T>::Init;
+  using OptionalStorageBase<T>::OptionalStorageBase;
+
+  OptionalStorage() = default;
+  OptionalStorage(OptionalStorage&& other) V8_NOEXCEPT = default;
+
+  OptionalStorage(const OptionalStorage& other) V8_NOEXCEPT {
+    if (other.is_populated_) Init(other.value_);
+  }
+};
+
+template <typename T>
+struct OptionalStorage<T, true /* trivially copy constructible */,
+                       true /* trivially move constructible */>
+    : OptionalStorageBase<T> {
+  // If both trivially {copy,move} constructible are true, it is not necessary
+  // to use user-defined constructors. So, just inheriting constructors
+  // from the base class works.
+  using OptionalStorageBase<T>::OptionalStorageBase;
+};
+
+// Base class to support conditionally usable copy-/move- constructors
+// and assign operators.
+template <typename T>
+class OptionalBase {
+  // This class provides implementation rather than public API, so everything
+  // should be hidden. Often we use composition, but we cannot in this case
+  // because of C++ language restriction.
+ protected:
+  constexpr OptionalBase() = default;
+  constexpr OptionalBase(const OptionalBase& other) V8_NOEXCEPT = default;
+  constexpr OptionalBase(OptionalBase&& other) V8_NOEXCEPT = default;
+
+  template <class... Args>
+  constexpr explicit OptionalBase(in_place_t, Args&&... args)
+      : storage_(in_place, std::forward<Args>(args)...) {}
+
+  // Implementation of converting constructors.
+  template <typename U>
+  explicit OptionalBase(const OptionalBase<U>& other) V8_NOEXCEPT {
+    if (other.storage_.is_populated_) storage_.Init(other.storage_.value_);
+  }
+
+  template <typename U>
+  explicit OptionalBase(OptionalBase<U>&& other) V8_NOEXCEPT {
+    if (other.storage_.is_populated_)
+      storage_.Init(std::move(other.storage_.value_));
+  }
+
+  ~OptionalBase() = default;
+
+  OptionalBase& operator=(const OptionalBase& other) V8_NOEXCEPT {
+    CopyAssign(other);
+    return *this;
+  }
+
+  OptionalBase& operator=(OptionalBase&& other) V8_NOEXCEPT {
+    MoveAssign(std::move(other));
+    return *this;
+  }
+
+  template <typename U>
+  void CopyAssign(const OptionalBase<U>& other) {
+    if (other.storage_.is_populated_)
+      InitOrAssign(other.storage_.value_);
+    else
+      FreeIfNeeded();
+  }
+
+  template <typename U>
+  void MoveAssign(OptionalBase<U>&& other) {
+    if (other.storage_.is_populated_)
+      InitOrAssign(std::move(other.storage_.value_));
+    else
+      FreeIfNeeded();
+  }
+
+  template <typename U>
+  void InitOrAssign(U&& value) {
+    if (storage_.is_populated_)
+      storage_.value_ = std::forward<U>(value);
+    else
+      storage_.Init(std::forward<U>(value));
+  }
+
+  void FreeIfNeeded() {
+    if (!storage_.is_populated_) return;
+    storage_.value_.~T();
+    storage_.is_populated_ = false;
+  }
+
+  // For implementing conversion, allow access to other typed OptionalBase
+  // class.
+  template <typename U>
+  friend class OptionalBase;
+
+  OptionalStorage<T> storage_;
+};
+
+// The following {Copy,Move}{Constructible,Assignable} structs are helpers to
+// implement constructor/assign-operator overloading. Specifically, if T is
+// is not movable but copyable, Optional<T>'s move constructor should not
+// participate in overload resolution. This inheritance trick implements that.
+template <bool is_copy_constructible>
+struct CopyConstructible {};
+
+template <>
+struct CopyConstructible<false> {
+  constexpr CopyConstructible() = default;
+  constexpr CopyConstructible(const CopyConstructible&) V8_NOEXCEPT = delete;
+  constexpr CopyConstructible(CopyConstructible&&) V8_NOEXCEPT = default;
+  CopyConstructible& operator=(const CopyConstructible&) V8_NOEXCEPT = default;
+  CopyConstructible& operator=(CopyConstructible&&) V8_NOEXCEPT = default;
+};
+
+template <bool is_move_constructible>
+struct MoveConstructible {};
+
+template <>
+struct MoveConstructible<false> {
+  constexpr MoveConstructible() = default;
+  constexpr MoveConstructible(const MoveConstructible&) V8_NOEXCEPT = default;
+  constexpr MoveConstructible(MoveConstructible&&) V8_NOEXCEPT = delete;
+  MoveConstructible& operator=(const MoveConstructible&) V8_NOEXCEPT = default;
+  MoveConstructible& operator=(MoveConstructible&&) V8_NOEXCEPT = default;
+};
+
+template <bool is_copy_assignable>
+struct CopyAssignable {};
+
+template <>
+struct CopyAssignable<false> {
+  constexpr CopyAssignable() = default;
+  constexpr CopyAssignable(const CopyAssignable&) V8_NOEXCEPT = default;
+  constexpr CopyAssignable(CopyAssignable&&) V8_NOEXCEPT = default;
+  CopyAssignable& operator=(const CopyAssignable&) V8_NOEXCEPT = delete;
+  CopyAssignable& operator=(CopyAssignable&&) V8_NOEXCEPT = default;
+};
+
+template <bool is_move_assignable>
+struct MoveAssignable {};
+
+template <>
+struct MoveAssignable<false> {
+  constexpr MoveAssignable() = default;
+  constexpr MoveAssignable(const MoveAssignable&) V8_NOEXCEPT = default;
+  constexpr MoveAssignable(MoveAssignable&&) V8_NOEXCEPT = default;
+  MoveAssignable& operator=(const MoveAssignable&) V8_NOEXCEPT = default;
+  MoveAssignable& operator=(MoveAssignable&&) V8_NOEXCEPT = delete;
+};
+
+// Helper to conditionally enable converting constructors and assign operators.
+template <typename T, typename U>
+struct IsConvertibleFromOptional
+    : std::integral_constant<
+          bool, std::is_constructible<T, Optional<U>&>::value ||
+                    std::is_constructible<T, const Optional<U>&>::value ||
+                    std::is_constructible<T, Optional<U>&&>::value ||
+                    std::is_constructible<T, const Optional<U>&&>::value ||
+                    std::is_convertible<Optional<U>&, T>::value ||
+                    std::is_convertible<const Optional<U>&, T>::value ||
+                    std::is_convertible<Optional<U>&&, T>::value ||
+                    std::is_convertible<const Optional<U>&&, T>::value> {};
+
+template <typename T, typename U>
+struct IsAssignableFromOptional
+    : std::integral_constant<
+          bool, IsConvertibleFromOptional<T, U>::value ||
+                    std::is_assignable<T&, Optional<U>&>::value ||
+                    std::is_assignable<T&, const Optional<U>&>::value ||
+                    std::is_assignable<T&, Optional<U>&&>::value ||
+                    std::is_assignable<T&, const Optional<U>&&>::value> {};
+
+// Forward compatibility for C++17.
+// Introduce one more deeper nested namespace to avoid leaking using std::swap.
+namespace swappable_impl {
+using std::swap;
+
+struct IsSwappableImpl {
+  // Tests if swap can be called. Check<T&>(0) returns true_type iff swap
+  // is available for T. Otherwise, Check's overload resolution falls back
+  // to Check(...) declared below thanks to SFINAE, so returns false_type.
+  template <typename T>
+  static auto Check(int i)
+      -> decltype(swap(std::declval<T>(), std::declval<T>()), std::true_type());
+
+  template <typename T>
+  static std::false_type Check(...);
+};
+}  // namespace swappable_impl
+
+template <typename T>
+struct IsSwappable : decltype(swappable_impl::IsSwappableImpl::Check<T&>(0)) {};
+
+// Forward compatibility for C++20.
+template <typename T>
+using RemoveCvRefT =
+    typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+
+}  // namespace internal
+
+// On Windows, by default, empty-base class optimization does not work,
+// which means even if the base class is empty struct, it still consumes one
+// byte for its body. __declspec(empty_bases) enables the optimization.
+// cf)
+// https://blogs.msdn.microsoft.com/vcblog/2016/03/30/optimizing-the-layout-of-empty-base-classes-in-vs2015-update-2-3/
+#ifdef OS_WIN
+#define OPTIONAL_DECLSPEC_EMPTY_BASES __declspec(empty_bases)
+#else
+#define OPTIONAL_DECLSPEC_EMPTY_BASES
+#endif
+
+// base::Optional is a Chromium version of the C++17 optional class:
+// std::optional documentation:
+// http://en.cppreference.com/w/cpp/utility/optional
+// Chromium documentation:
+// https://chromium.googlesource.com/chromium/src/+/master/docs/optional.md
+//
+// These are the differences between the specification and the implementation:
+// - Constructors do not use 'constexpr' as it is a C++14 extension.
+// - 'constexpr' might be missing in some places for reasons specified locally.
+// - No exceptions are thrown, because they are banned from Chromium.
+//   All copy/move constructors or assignment operators are marked V8_NOEXCEPT.
+// - All the non-members are in the 'base' namespace instead of 'std'.
+//
+// Note that T cannot have a constructor T(Optional<T>) etc. Optional<T> checks
+// T's constructor (specifically via IsConvertibleFromOptional), and in the
+// check whether T can be constructible from Optional<T>, which is recursive
+// so it does not work. As of Feb 2018, std::optional C++17 implementation in
+// both clang and gcc has same limitation. MSVC SFINAE looks to have different
+// behavior, but anyway it reports an error, too.
 template <typename T>
-using Optional = absl::optional<T>;
-using absl::in_place;
-using absl::in_place_t;
-using absl::make_optional;
-using absl::nullopt;
-using absl::nullopt_t;
+class OPTIONAL_DECLSPEC_EMPTY_BASES Optional
+    : public internal::OptionalBase<T>,
+      public internal::CopyConstructible<std::is_copy_constructible<T>::value>,
+      public internal::MoveConstructible<std::is_move_constructible<T>::value>,
+      public internal::CopyAssignable<std::is_copy_constructible<T>::value &&
+                                      std::is_copy_assignable<T>::value>,
+      public internal::MoveAssignable<std::is_move_constructible<T>::value &&
+                                      std::is_move_assignable<T>::value> {
+ public:
+#undef OPTIONAL_DECLSPEC_EMPTY_BASES
+  using value_type = T;
+
+  // Defer default/copy/move constructor implementation to OptionalBase.
+  constexpr Optional() = default;
+  constexpr Optional(const Optional& other) V8_NOEXCEPT = default;
+  constexpr Optional(Optional&& other) V8_NOEXCEPT = default;
+
+  constexpr Optional(nullopt_t) {}  // NOLINT(runtime/explicit)
+
+  // Converting copy constructor. "explicit" only if
+  // std::is_convertible<const U&, T>::value is false. It is implemented by
+  // declaring two almost same constructors, but that condition in enable_if
+  // is different, so that either one is chosen, thanks to SFINAE.
+  template <typename U,
+            typename std::enable_if<
+                std::is_constructible<T, const U&>::value &&
+                    !internal::IsConvertibleFromOptional<T, U>::value &&
+                    std::is_convertible<const U&, T>::value,
+                bool>::type = false>
+  Optional(const Optional<U>& other) V8_NOEXCEPT
+      : internal::OptionalBase<T>(other) {}
+
+  template <typename U,
+            typename std::enable_if<
+                std::is_constructible<T, const U&>::value &&
+                    !internal::IsConvertibleFromOptional<T, U>::value &&
+                    !std::is_convertible<const U&, T>::value,
+                bool>::type = false>
+  explicit Optional(const Optional<U>& other) V8_NOEXCEPT
+      : internal::OptionalBase<T>(other) {}
+
+  // Converting move constructor. Similar to converting copy constructor,
+  // declaring two (explicit and non-explicit) constructors.
+  template <typename U,
+            typename std::enable_if<
+                std::is_constructible<T, U&&>::value &&
+                    !internal::IsConvertibleFromOptional<T, U>::value &&
+                    std::is_convertible<U&&, T>::value,
+                bool>::type = false>
+  Optional(Optional<U>&& other) V8_NOEXCEPT
+      : internal::OptionalBase<T>(std::move(other)) {}
+
+  template <typename U,
+            typename std::enable_if<
+                std::is_constructible<T, U&&>::value &&
+                    !internal::IsConvertibleFromOptional<T, U>::value &&
+                    !std::is_convertible<U&&, T>::value,
+                bool>::type = false>
+  explicit Optional(Optional<U>&& other) V8_NOEXCEPT
+      : internal::OptionalBase<T>(std::move(other)) {}
+
+  template <class... Args>
+  constexpr explicit Optional(in_place_t, Args&&... args)
+      : internal::OptionalBase<T>(in_place, std::forward<Args>(args)...) {}
+
+  template <class U, class... Args,
+            class = typename std::enable_if<std::is_constructible<
+                value_type, std::initializer_list<U>&, Args...>::value>::type>
+  constexpr explicit Optional(in_place_t, std::initializer_list<U> il,
+                              Args&&... args)
+      : internal::OptionalBase<T>(in_place, il, std::forward<Args>(args)...) {}
+
+  // Forward value constructor. Similar to converting constructors,
+  // conditionally explicit.
+  template <
+      typename U = value_type,
+      typename std::enable_if<
+          std::is_constructible<T, U&&>::value &&
+              !std::is_same<internal::RemoveCvRefT<U>, in_place_t>::value &&
+              !std::is_same<internal::RemoveCvRefT<U>, Optional<T>>::value &&
+              std::is_convertible<U&&, T>::value,
+          bool>::type = false>
+  constexpr Optional(U&& value)  // NOLINT(runtime/explicit)
+      : internal::OptionalBase<T>(in_place, std::forward<U>(value)) {}
+
+  template <
+      typename U = value_type,
+      typename std::enable_if<
+          std::is_constructible<T, U&&>::value &&
+              !std::is_same<internal::RemoveCvRefT<U>, in_place_t>::value &&
+              !std::is_same<internal::RemoveCvRefT<U>, Optional<T>>::value &&
+              !std::is_convertible<U&&, T>::value,
+          bool>::type = false>
+  constexpr explicit Optional(U&& value)
+      : internal::OptionalBase<T>(in_place, std::forward<U>(value)) {}
+
+  ~Optional() = default;
+
+  // Defer copy-/move- assign operator implementation to OptionalBase.
+  Optional& operator=(const Optional& other) V8_NOEXCEPT = default;
+  Optional& operator=(Optional&& other) V8_NOEXCEPT = default;
+
+  Optional& operator=(nullopt_t) {
+    FreeIfNeeded();
+    return *this;
+  }
+
+  // Perfect-forwarded assignment.
+  template <typename U>
+  typename std::enable_if<
+      !std::is_same<internal::RemoveCvRefT<U>, Optional<T>>::value &&
+          std::is_constructible<T, U>::value &&
+          std::is_assignable<T&, U>::value &&
+          (!std::is_scalar<T>::value ||
+           !std::is_same<typename std::decay<U>::type, T>::value),
+      Optional&>::type
+  operator=(U&& value) V8_NOEXCEPT {
+    InitOrAssign(std::forward<U>(value));
+    return *this;
+  }
+
+  // Copy assign the state of other.
+  template <typename U>
+  typename std::enable_if<!internal::IsAssignableFromOptional<T, U>::value &&
+                              std::is_constructible<T, const U&>::value &&
+                              std::is_assignable<T&, const U&>::value,
+                          Optional&>::type
+  operator=(const Optional<U>& other) V8_NOEXCEPT {
+    CopyAssign(other);
+    return *this;
+  }
+
+  // Move assign the state of other.
+  template <typename U>
+  typename std::enable_if<!internal::IsAssignableFromOptional<T, U>::value &&
+                              std::is_constructible<T, U>::value &&
+                              std::is_assignable<T&, U>::value,
+                          Optional&>::type
+  operator=(Optional<U>&& other) V8_NOEXCEPT {
+    MoveAssign(std::move(other));
+    return *this;
+  }
+
+  constexpr const T* operator->() const {
+    DCHECK(storage_.is_populated_);
+    return &storage_.value_;
+  }
+
+  constexpr T* operator->() {
+    DCHECK(storage_.is_populated_);
+    return &storage_.value_;
+  }
+
+  constexpr const T& operator*() const& {
+    DCHECK(storage_.is_populated_);
+    return storage_.value_;
+  }
+
+  constexpr T& operator*() & {
+    DCHECK(storage_.is_populated_);
+    return storage_.value_;
+  }
+
+  constexpr const T&& operator*() const&& {
+    DCHECK(storage_.is_populated_);
+    return std::move(storage_.value_);
+  }
+
+  constexpr T&& operator*() && {
+    DCHECK(storage_.is_populated_);
+    return std::move(storage_.value_);
+  }
+
+  constexpr explicit operator bool() const { return storage_.is_populated_; }
+
+  constexpr bool has_value() const { return storage_.is_populated_; }
+
+  T& value() & {
+    CHECK(storage_.is_populated_);
+    return storage_.value_;
+  }
+
+  const T& value() const & {
+    CHECK(storage_.is_populated_);
+    return storage_.value_;
+  }
+
+  T&& value() && {
+    CHECK(storage_.is_populated_);
+    return std::move(storage_.value_);
+  }
+
+  const T&& value() const && {
+    CHECK(storage_.is_populated_);
+    return std::move(storage_.value_);
+  }
+
+  template <class U>
+  constexpr T value_or(U&& default_value) const & {
+    // TODO(mlamouri): add the following assert when possible:
+    // static_assert(std::is_copy_constructible<T>::value,
+    //               "T must be copy constructible");
+    static_assert(std::is_convertible<U, T>::value,
+                  "U must be convertible to T");
+    return storage_.is_populated_
+               ? storage_.value_
+               : static_cast<T>(std::forward<U>(default_value));
+  }
+
+  template <class U>
+  T value_or(U&& default_value) && {
+    // TODO(mlamouri): add the following assert when possible:
+    // static_assert(std::is_move_constructible<T>::value,
+    //               "T must be move constructible");
+    static_assert(std::is_convertible<U, T>::value,
+                  "U must be convertible to T");
+    return storage_.is_populated_
+               ? std::move(storage_.value_)
+               : static_cast<T>(std::forward<U>(default_value));
+  }
+
+  void swap(Optional& other) {
+    if (!storage_.is_populated_ && !other.storage_.is_populated_) return;
+
+    if (storage_.is_populated_ != other.storage_.is_populated_) {
+      if (storage_.is_populated_) {
+        other.storage_.Init(std::move(storage_.value_));
+        FreeIfNeeded();
+      } else {
+        storage_.Init(std::move(other.storage_.value_));
+        other.FreeIfNeeded();
+      }
+      return;
+    }
+
+    DCHECK(storage_.is_populated_ && other.storage_.is_populated_);
+    using std::swap;
+    swap(**this, *other);
+  }
+
+  void reset() { FreeIfNeeded(); }
+
+  template <class... Args>
+  T& emplace(Args&&... args) {
+    FreeIfNeeded();
+    storage_.Init(std::forward<Args>(args)...);
+    return storage_.value_;
+  }
+
+  template <class U, class... Args>
+  typename std::enable_if<
+      std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value,
+      T&>::type
+  emplace(std::initializer_list<U> il, Args&&... args) {
+    FreeIfNeeded();
+    storage_.Init(il, std::forward<Args>(args)...);
+    return storage_.value_;
+  }
+
+ private:
+  // Accessing template base class's protected member needs explicit
+  // declaration to do so.
+  using internal::OptionalBase<T>::CopyAssign;
+  using internal::OptionalBase<T>::FreeIfNeeded;
+  using internal::OptionalBase<T>::InitOrAssign;
+  using internal::OptionalBase<T>::MoveAssign;
+  using internal::OptionalBase<T>::storage_;
+};
+
+// Here after defines comparation operators. The definition follows
+// http://en.cppreference.com/w/cpp/utility/optional/operator_cmp
+// while bool() casting is replaced by has_value() to meet the chromium
+// style guide.
+template <class T, class U>
+bool operator==(const Optional<T>& lhs, const Optional<U>& rhs) {
+  if (lhs.has_value() != rhs.has_value()) return false;
+  if (!lhs.has_value()) return true;
+  return *lhs == *rhs;
+}
+
+template <class T, class U>
+bool operator!=(const Optional<T>& lhs, const Optional<U>& rhs) {
+  if (lhs.has_value() != rhs.has_value()) return true;
+  if (!lhs.has_value()) return false;
+  return *lhs != *rhs;
+}
+
+template <class T, class U>
+bool operator<(const Optional<T>& lhs, const Optional<U>& rhs) {
+  if (!rhs.has_value()) return false;
+  if (!lhs.has_value()) return true;
+  return *lhs < *rhs;
+}
+
+template <class T, class U>
+bool operator<=(const Optional<T>& lhs, const Optional<U>& rhs) {
+  if (!lhs.has_value()) return true;
+  if (!rhs.has_value()) return false;
+  return *lhs <= *rhs;
+}
+
+template <class T, class U>
+bool operator>(const Optional<T>& lhs, const Optional<U>& rhs) {
+  if (!lhs.has_value()) return false;
+  if (!rhs.has_value()) return true;
+  return *lhs > *rhs;
+}
+
+template <class T, class U>
+bool operator>=(const Optional<T>& lhs, const Optional<U>& rhs) {
+  if (!rhs.has_value()) return true;
+  if (!lhs.has_value()) return false;
+  return *lhs >= *rhs;
+}
+
+template <class T>
+constexpr bool operator==(const Optional<T>& opt, nullopt_t) {
+  return !opt;
+}
+
+template <class T>
+constexpr bool operator==(nullopt_t, const Optional<T>& opt) {
+  return !opt;
+}
+
+template <class T>
+constexpr bool operator!=(const Optional<T>& opt, nullopt_t) {
+  return opt.has_value();
+}
+
+template <class T>
+constexpr bool operator!=(nullopt_t, const Optional<T>& opt) {
+  return opt.has_value();
+}
+
+template <class T>
+constexpr bool operator<(const Optional<T>& opt, nullopt_t) {
+  return false;
+}
+
+template <class T>
+constexpr bool operator<(nullopt_t, const Optional<T>& opt) {
+  return opt.has_value();
+}
+
+template <class T>
+constexpr bool operator<=(const Optional<T>& opt, nullopt_t) {
+  return !opt;
+}
+
+template <class T>
+constexpr bool operator<=(nullopt_t, const Optional<T>& opt) {
+  return true;
+}
+
+template <class T>
+constexpr bool operator>(const Optional<T>& opt, nullopt_t) {
+  return opt.has_value();
+}
+
+template <class T>
+constexpr bool operator>(nullopt_t, const Optional<T>& opt) {
+  return false;
+}
+
+template <class T>
+constexpr bool operator>=(const Optional<T>& opt, nullopt_t) {
+  return true;
+}
+
+template <class T>
+constexpr bool operator>=(nullopt_t, const Optional<T>& opt) {
+  return !opt;
+}
+
+template <class T, class U>
+constexpr bool operator==(const Optional<T>& opt, const U& value) {
+  return opt.has_value() ? *opt == value : false;
+}
+
+template <class T, class U>
+constexpr bool operator==(const U& value, const Optional<T>& opt) {
+  return opt.has_value() ? value == *opt : false;
+}
+
+template <class T, class U>
+constexpr bool operator!=(const Optional<T>& opt, const U& value) {
+  return opt.has_value() ? *opt != value : true;
+}
+
+template <class T, class U>
+constexpr bool operator!=(const U& value, const Optional<T>& opt) {
+  return opt.has_value() ? value != *opt : true;
+}
+
+template <class T, class U>
+constexpr bool operator<(const Optional<T>& opt, const U& value) {
+  return opt.has_value() ? *opt < value : true;
+}
+
+template <class T, class U>
+constexpr bool operator<(const U& value, const Optional<T>& opt) {
+  return opt.has_value() ? value < *opt : false;
+}
+
+template <class T, class U>
+constexpr bool operator<=(const Optional<T>& opt, const U& value) {
+  return opt.has_value() ? *opt <= value : true;
+}
+
+template <class T, class U>
+constexpr bool operator<=(const U& value, const Optional<T>& opt) {
+  return opt.has_value() ? value <= *opt : false;
+}
+
+template <class T, class U>
+constexpr bool operator>(const Optional<T>& opt, const U& value) {
+  return opt.has_value() ? *opt > value : false;
+}
+
+template <class T, class U>
+constexpr bool operator>(const U& value, const Optional<T>& opt) {
+  return opt.has_value() ? value > *opt : true;
+}
+
+template <class T, class U>
+constexpr bool operator>=(const Optional<T>& opt, const U& value) {
+  return opt.has_value() ? *opt >= value : false;
+}
+
+template <class T, class U>
+constexpr bool operator>=(const U& value, const Optional<T>& opt) {
+  return opt.has_value() ? value >= *opt : true;
+}
+
+template <class T>
+constexpr Optional<typename std::decay<T>::type> make_optional(T&& value) {
+  return Optional<typename std::decay<T>::type>(std::forward<T>(value));
+}
+
+template <class T, class... Args>
+constexpr Optional<T> make_optional(Args&&... args) {
+  return Optional<T>(in_place, std::forward<Args>(args)...);
+}
+
+template <class T, class U, class... Args>
+constexpr Optional<T> make_optional(std::initializer_list<U> il,
+                                    Args&&... args) {
+  return Optional<T>(in_place, il, std::forward<Args>(args)...);
+}
+
+// Partial specialization for a function template is not allowed. Also, it is
+// not allowed to add overload function to std namespace, while it is allowed
+// to specialize the template in std. Thus, swap() (kind of) overloading is
+// defined in base namespace, instead.
+template <class T>
+typename std::enable_if<std::is_move_constructible<T>::value &&
+                        internal::IsSwappable<T>::value>::type
+swap(Optional<T>& lhs, Optional<T>& rhs) {
+  lhs.swap(rhs);
+}
 
 }  // namespace base
 }  // namespace v8

test/wasm-api-tests/BUILD.gn

@@ -9,7 +9,6 @@ v8_executable("wasm_api_tests") {
 
   deps = [
     "../:common_test_headers",
-    "../..:v8_abseil",
     "../..:v8_internal_headers",
     "../..:v8_maybe_icu",
     "../..:wee8",

tools/gcmole/BUILD.gn

@@ -26,7 +26,6 @@ group("v8_run_gcmole") {
     "../../test/cctest/",
     "../../test/common/",
     "../../testing/gtest/include/gtest/gtest_prod.h",
-    "../../third_party/abseil-cpp/",
     "../../third_party/googletest/src/googletest/include/gtest/gtest_prod.h",
     "../../third_party/icu/source/",
     "../../third_party/wasm-api/wasm.h",

tools/gcmole/gcmole.py

@@ -103,7 +103,6 @@ def MakeClangCommandLine(plugin, plugin_args, arch_cfg, clang_bin_dir,
       "-I./",
       "-Iinclude/",
       "-Iout/build/gen",
-      "-Ithird_party/abseil-cpp",
       "-Ithird_party/icu/source/common",
       "-Ithird_party/icu/source/i18n",
   ] + arch_cfg.arch_options)