Revert "cppgc-js: Add snapshot for C++ objects"

This reverts commit 02849fd9.

Reason for revert: Breaks Win64 MSVC bot and closes the tree - https://ci.chromium.org/p/v8/builders/ci/V8%20Win64%20-%20msvc/15416

Original change's description:
> cppgc-js: Add snapshot for C++ objects
>
> The following implements a snapshotting algorithm for C++ objects that
> also filters strongly-connected components (SCCs) of only "hidden"
> objects that are not (transitively) referencing any non-hidden
> objects.
>
> C++ objects come in two versions.
> a. Named objects that have been assigned a name through NameProvider.
> b. Unnamed objects, that are potentially hidden if the build
>    configuration requires Oilpan to hide such names. Hidden objects have
>    their name set to NameProvider::kHiddenName.
>
> The main challenge for the algorithm is to avoid blowing up the final
> object graph with hidden nodes that do not carry information. For that
> reason, the algorithm filters SCCs of only hidden objects, e.g.:
>   ...  -> (object) -> (object) -> (hidden) -> (hidden)
> In this case the (hidden) objects are filtered from the graph. The
> trickiest part is maintaining visibility state for objects referencing
> other objects that are currently being processed.
>
> Main algorithm idea (two passes):
> 1. First pass marks all non-hidden objects and those that transitively
>    reach non-hidden objects as visible. Details:
>    - Iterate over all objects.
>    - If object is non-hidden mark it as visible and also mark parent
>      as visible if needed.
>    - If object is hidden, traverse children as DFS to find non-hidden
>      objects. Post-order process the objects and mark those objects as
>      visible that have child nodes that are visible themselves.
>    - Maintain an epoch counter (StateStorage::state_count_) to allow
>      deferring the visibility decision to other objects in the same
>      SCC. This is similar to the "lowlink" value in Tarjan's algorithm
>      for SCC.
>    - After the first pass it is guaranteed that all deferred
>      visibility decisions can be resolved.
> 2. Second pass adds nodes and edges for all visible objects.
>    - Upon first checking the visibility state of an object, all deferred
>      visibility states are resolved.
>
> For practical reasons, the recursion is transformed into an iteration.
> We do not use plain Tarjan's algorithm to avoid another pass over
> all nodes to create SCCs.
>
> Follow ups:
> 1. Adding wrapper nodes for cpp objects that are wrappables for V8
>    wrappers.
> 2. Adding detachedness information.
>
> Change-Id: I6e127d2c6d65e77defe08e39295a2594f463b962
> Bug: chromium:1056170
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2467854
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#70567}

TBR=ulan@chromium.org,mlippautz@chromium.org,bikineev@chromium.org,omerkatz@chromium.org

Change-Id: I64a2cf2259bdaed81f6e0f92bdcc7a1f0df4d197
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2479471Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70571}

BUILD.gn

@@ -2593,8 +2593,6 @@ v8_source_set("v8_base_without_compiler") {
     "src/heap/concurrent-marking.h",
     "src/heap/cppgc-js/cpp-heap.cc",
     "src/heap/cppgc-js/cpp-heap.h",
-    "src/heap/cppgc-js/cpp-snapshot.cc",
-    "src/heap/cppgc-js/cpp-snapshot.h",
     "src/heap/cppgc-js/unified-heap-marking-state.h",
     "src/heap/cppgc-js/unified-heap-marking-visitor.cc",
     "src/heap/cppgc-js/unified-heap-marking-visitor.h",

src/heap/cppgc-js/cpp-heap.cc

@@ -12,7 +12,6 @@
 #include "src/execution/isolate.h"
 #include "src/flags/flags.h"
 #include "src/heap/base/stack.h"
-#include "src/heap/cppgc-js/cpp-snapshot.h"
 #include "src/heap/cppgc-js/unified-heap-marking-state.h"
 #include "src/heap/cppgc-js/unified-heap-marking-visitor.h"
 #include "src/heap/cppgc/concurrent-marker.h"
@@ -29,7 +28,6 @@
 #include "src/heap/marking-worklist.h"
 #include "src/heap/sweeper.h"
 #include "src/init/v8.h"
-#include "src/profiler/heap-profiler.h"
 
 namespace v8 {
 namespace internal {
@@ -148,13 +146,6 @@ CppHeap::CppHeap(
                                     kSupportsConservativeStackScan),
       isolate_(*reinterpret_cast<Isolate*>(isolate)) {
   CHECK(!FLAG_incremental_marking_wrappers);
-  isolate_.heap_profiler()->AddBuildEmbedderGraphCallback(&CppGraphBuilder::Run,
-                                                          this);
-}
-
-CppHeap::~CppHeap() {
-  isolate_.heap_profiler()->RemoveBuildEmbedderGraphCallback(
-      &CppGraphBuilder::Run, this);
 }
 
 void CppHeap::RegisterV8References(

src/heap/cppgc-js/cpp-heap.h

@@ -22,7 +22,6 @@ class V8_EXPORT_PRIVATE CppHeap final : public cppgc::internal::HeapBase,
   CppHeap(v8::Isolate* isolate,
           const std::vector<std::unique_ptr<cppgc::CustomSpaceBase>>&
               custom_spaces);
-  ~CppHeap() final;
 
   CppHeap(const CppHeap&) = delete;
   CppHeap& operator=(const CppHeap&) = delete;

src/heap/cppgc-js/cpp-snapshot.h

-// Copyright 2020 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef V8_HEAP_CPPGC_JS_CPP_SNAPSHOT_H_
-#define V8_HEAP_CPPGC_JS_CPP_SNAPSHOT_H_
-
-#include "src/base/macros.h"
-
-namespace v8 {
-
-class Isolate;
-class EmbedderGraph;
-
-namespace internal {
-
-class V8_EXPORT_PRIVATE CppGraphBuilder final {
- public:
-  // Add the C++ snapshot to the existing |graph|. See CppGraphBuilderImpl for
-  // algorithm internals.
-  static void Run(v8::Isolate* isolate, v8::EmbedderGraph* graph, void* data);
-
-  CppGraphBuilder() = delete;
-};
-
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_HEAP_CPPGC_JS_CPP_SNAPSHOT_H_

src/profiler/heap-snapshot-generator.cc

@@ -103,8 +103,8 @@ void HeapEntry::SetNamedAutoIndexReference(HeapGraphEdge::Type type,
   SetNamedReference(type, name, child);
 }
 
-void HeapEntry::Print(const char* prefix, const char* edge_name, int max_depth,
-                      int indent) const {
+void HeapEntry::Print(
+    const char* prefix, const char* edge_name, int max_depth, int indent) {
   STATIC_ASSERT(sizeof(unsigned) == sizeof(id()));
   base::OS::Print("%6zu @%6u %*c %s%s: ", self_size(), id(), indent, ' ',
                   prefix, edge_name);
@@ -162,7 +162,7 @@ void HeapEntry::Print(const char* prefix, const char* edge_name, int max_depth,
   }
 }
 
-const char* HeapEntry::TypeAsString() const {
+const char* HeapEntry::TypeAsString() {
   switch (type()) {
     case kHidden: return "/hidden/";
     case kObject: return "/object/";

src/profiler/heap-snapshot-generator.h

@@ -151,12 +151,12 @@ class HeapEntry {
                                   StringsStorage* strings);
 
   V8_EXPORT_PRIVATE void Print(const char* prefix, const char* edge_name,
-                               int max_depth, int indent) const;
+                               int max_depth, int indent);
 
  private:
   V8_INLINE std::vector<HeapGraphEdge*>::iterator children_begin() const;
   V8_INLINE std::vector<HeapGraphEdge*>::iterator children_end() const;
-  const char* TypeAsString() const;
+  const char* TypeAsString();
 
   unsigned type_: 4;
   unsigned index_ : 28;  // Supports up to ~250M objects.
@@ -196,9 +196,7 @@ class HeapSnapshot {
     return gc_subroot_entries_[static_cast<int>(root)];
   }
   std::deque<HeapEntry>& entries() { return entries_; }
-  const std::deque<HeapEntry>& entries() const { return entries_; }
   std::deque<HeapGraphEdge>& edges() { return edges_; }
-  const std::deque<HeapGraphEdge>& edges() const { return edges_; }
   std::vector<HeapGraphEdge*>& children() { return children_; }
   const std::vector<SourceLocation>& locations() const { return locations_; }
   void RememberLastJSObjectId();

test/unittests/BUILD.gn

@@ -297,7 +297,6 @@ v8_source_set("unittests_sources") {
     "heap/safepoint-unittest.cc",
     "heap/slot-set-unittest.cc",
     "heap/spaces-unittest.cc",
-    "heap/unified-heap-snapshot-unittest.cc",
     "heap/unified-heap-unittest.cc",
     "heap/unmapper-unittest.cc",
     "heap/worklist-unittest.cc",