Reland "cppgc: Add tests for in-construction during ctor"

This is a reland of 62ff82e4

Original change's description:
> cppgc: Add tests for in-construction during ctor
>
> Adds explicit tests that check that an object is marked as in
> construction while running the constructor.
>
> Bug: chromium:1056170
> Change-Id: I7f7340832e1bc31cec98784c261ed86deb402e72
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2811238
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73869}

Bug: chromium:1056170
Change-Id: I38c8579dc2ed437f2ad530bd552b5ef037ba8621
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2817603
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73880}

test/unittests/heap/cppgc/garbage-collected-unittest.cc

@@ -6,6 +6,7 @@
 
 #include "include/cppgc/allocation.h"
 #include "include/cppgc/type-traits.h"
+#include "src/base/platform/mutex.h"
 #include "src/heap/cppgc/heap-object-header.h"
 #include "src/heap/cppgc/heap.h"
 #include "test/unittests/heap/cppgc/tests.h"
@@ -156,5 +157,86 @@ TEST_F(GarbageCollectedTestWithHeap, PostConstructionCallbackForMixin) {
   EXPECT_EQ(1u, MixinWithPostConstructionCallback::cb_callcount);
 }
 
+namespace {
+
+int GetDummyValue() {
+  static v8::base::Mutex mutex;
+  static int ret = 43;
+  // Global lock access to avoid reordering.
+  v8::base::MutexGuard guard(&mutex);
+  return ret;
+}
+
+class CheckObjectInConstructionBeforeInitializerList final
+    : public GarbageCollected<CheckObjectInConstructionBeforeInitializerList> {
+ public:
+  CheckObjectInConstructionBeforeInitializerList()
+      : in_construction_before_initializer_list_(
+            HeapObjectHeader::FromPayload(this).IsInConstruction()),
+        unused_int_(GetDummyValue()) {
+    EXPECT_TRUE(in_construction_before_initializer_list_);
+    EXPECT_TRUE(HeapObjectHeader::FromPayload(this).IsInConstruction());
+  }
+
+  void Trace(Visitor*) const {}
+
+ private:
+  bool in_construction_before_initializer_list_;
+  int unused_int_;
+};
+
+class CheckMixinInConstructionBeforeInitializerList
+    : public GarbageCollectedMixin {
+ public:
+  explicit CheckMixinInConstructionBeforeInitializerList(void* payload_start)
+      : in_construction_before_initializer_list_(
+            HeapObjectHeader::FromPayload(payload_start).IsInConstruction()),
+        unused_int_(GetDummyValue()) {
+    EXPECT_TRUE(in_construction_before_initializer_list_);
+    EXPECT_TRUE(
+        HeapObjectHeader::FromPayload(payload_start).IsInConstruction());
+  }
+
+  void Trace(Visitor*) const override {}
+
+ private:
+  bool in_construction_before_initializer_list_;
+  int unused_int_;
+};
+
+class UnmanagedMixinForcingVTable {
+ protected:
+  virtual void ForceVTable() {}
+};
+
+class CheckGCedWithMixinInConstructionBeforeInitializerList
+    : public GarbageCollected<
+          CheckGCedWithMixinInConstructionBeforeInitializerList>,
+      public UnmanagedMixinForcingVTable,
+      public CheckMixinInConstructionBeforeInitializerList {
+ public:
+  CheckGCedWithMixinInConstructionBeforeInitializerList()
+      : CheckMixinInConstructionBeforeInitializerList(this) {
+    // Ensure that compiler indeed generated an inner object.
+    CHECK_NE(
+        this,
+        static_cast<void*>(
+            static_cast<CheckMixinInConstructionBeforeInitializerList*>(this)));
+  }
+};
+
+}  // namespace
+
+TEST_F(GarbageCollectedTestWithHeap, GarbageCollectedInConstructionDuringCtor) {
+  MakeGarbageCollected<CheckObjectInConstructionBeforeInitializerList>(
+      GetAllocationHandle());
+}
+
+TEST_F(GarbageCollectedTestWithHeap,
+       GarbageCollectedMixinInConstructionDuringCtor) {
+  MakeGarbageCollected<CheckGCedWithMixinInConstructionBeforeInitializerList>(
+      GetAllocationHandle());
+}
+
 }  // namespace internal
 }  // namespace cppgc