bindings: Fix TraceWrapperV8Reference in HeapVector and ephemerons

- Allow TraceWrapperV8Reference in HeapVector (previously, the test
  would not compile)
- Fix usage of TraceWrapperV8Reference in ephemerons

Change-Id: I1430307a5c8692a7fa38fd4857be391c2a243a26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1886857
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710449}

third_party/blink/renderer/bindings/core/v8/trace_wrapper_v8_reference_test.cc

@@ -197,4 +197,50 @@ TEST_F(TraceWrapperV8ReferenceTest, MoveOverNonEmpty) {
   CHECK(observer1.IsEmpty());
 }
 
+TEST_F(TraceWrapperV8ReferenceTest, HeapVector) {
+  V8TestingScope testing_scope;
+  SetIsolate(testing_scope.GetIsolate());
+
+  using VectorContainer = HeapVector<TraceWrapperV8Reference<v8::Value>>;
+  Persistent<VectorContainer> holder(MakeGarbageCollected<VectorContainer>());
+  v8::Persistent<v8::Value> observer;
+  {
+    v8::HandleScope handle_scope(GetIsolate());
+    v8::Local<v8::Value> value = v8::Object::New(GetIsolate());
+    observer.Reset(GetIsolate(), value);
+    observer.SetWeak();
+    holder->push_back(TraceWrapperV8Reference<v8::Value>(GetIsolate(), value));
+  }
+  RunV8FullGC();
+  CHECK(!observer.IsEmpty());
+  holder.Clear();
+  RunV8FullGC();
+  CHECK(observer.IsEmpty());
+}
+
+TEST_F(TraceWrapperV8ReferenceTest, Ephemeron) {
+  V8TestingScope testing_scope;
+  SetIsolate(testing_scope.GetIsolate());
+
+  using EphemeronMap = HeapHashMap<WeakMember<TraceWrapperV8ReferenceHolder>,
+                                   TraceWrapperV8Reference<v8::Value>>;
+  Persistent<EphemeronMap> holder(MakeGarbageCollected<EphemeronMap>());
+  v8::Persistent<v8::Value> observer;
+  Persistent<TraceWrapperV8ReferenceHolder> object(
+      MakeGarbageCollected<TraceWrapperV8ReferenceHolder>());
+  {
+    v8::HandleScope handle_scope(GetIsolate());
+    v8::Local<v8::Value> value = v8::Object::New(GetIsolate());
+    observer.Reset(GetIsolate(), value);
+    observer.SetWeak();
+    holder->insert(WeakMember<TraceWrapperV8ReferenceHolder>(object),
+                   TraceWrapperV8Reference<v8::Value>(GetIsolate(), value));
+  }
+  RunV8FullGC();
+  EXPECT_TRUE(!observer.IsEmpty());
+  holder.Clear();
+  RunV8FullGC();
+  CHECK(observer.IsEmpty());
+}
+
 }  // namespace blink

third_party/blink/renderer/platform/bindings/trace_wrapper_v8_reference.h

@@ -120,4 +120,25 @@ class TraceWrapperV8Reference {
 
 }  // namespace blink
 
+namespace WTF {
+
+template <typename T>
+struct IsTraceable<blink::TraceWrapperV8Reference<T>> {
+  STATIC_ONLY(IsTraceable);
+  static const bool value = true;
+};
+
+template <typename T>
+struct VectorTraits<blink::TraceWrapperV8Reference<T>>
+    : VectorTraitsBase<blink::TraceWrapperV8Reference<T>> {
+  STATIC_ONLY(VectorTraits);
+  static const bool kNeedsDestruction = false;
+  static const bool kCanInitializeWithMemset = true;
+  static const bool kCanClearUnusedSlotsWithMemset = true;
+  static const bool kCanCopyWithMemcpy = false;
+  static const bool kCanMoveWithMemcpy = false;
+};
+
+}  // namespace WTF
+
 #endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_BINDINGS_TRACE_WRAPPER_V8_REFERENCE_H_