[heap] Address left-over comments on CL

Bug: v8:8557
Change-Id: If6e70c30c0553f8742980590875c4892535e5863
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1559749Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60741}

src/objects/js-objects.cc

@@ -2553,6 +2553,7 @@ bool JSObject::IsUnmodifiedApiObject(FullObjectSlot o) {
   if (!maybe_constructor->IsJSFunction()) return false;
   JSFunction constructor = JSFunction::cast(maybe_constructor);
   if (js_object->elements()->length() != 0) return false;
+  // Check that the object is not a key in a WeakMap (over-approximation).
   if (!js_object->GetIdentityHash()->IsUndefined()) return false;
 
   return constructor->initial_map() == heap_object->map();

test/cctest/test-global-handles.cc

@@ -312,14 +312,19 @@ TEST(WeakHandleToUnmodifiedJSApiObjectDiesOnScavenge) {
 
 TEST(WeakHandleToJSApiObjectWithIdentityHashSurvivesScavenge) {
   CcTest::InitializeVM();
+  Isolate* i_isolate = CcTest::i_isolate();
+  HandleScope scope(i_isolate);
+  Handle<JSWeakMap> weakmap = i_isolate->factory()->NewJSWeakMap();
+
   WeakHandleTest(
       CcTest::isolate(), &ConstructJSApiObject,
-      [](FlagAndPersistent* fp) {
+      [&weakmap, i_isolate](FlagAndPersistent* fp) {
         v8::HandleScope scope(CcTest::isolate());
-        v8::Local<v8::Object> handle =
-            v8::Local<v8::Object>::New(CcTest::isolate(), fp->handle);
-        handle->GetIdentityHash();
-        handle.Clear();
+        Handle<JSReceiver> key =
+            Utils::OpenHandle(*fp->handle.Get(CcTest::isolate()));
+        Handle<Smi> smi(Smi::FromInt(23), i_isolate);
+        int32_t hash = key->GetOrCreateHash(i_isolate)->value();
+        JSWeakCollection::Set(weakmap, key, smi, hash);
       },
       []() { InvokeScavenge(); }, SurvivalMode::kSurvives);
 }