cppgc: Object sizes for cpp objects in heap snapshot

This CL sets it so that the actual object size is reported only when
cppgc_enable_object_names is set to true. Otherwise the heap snapshot
merges nodes and the sizes don't make sense.

Also, this will resolve a web test failure for the library.

Bug: chromium:1056170
Change-Id: I32f6552560bdfad4b64c67b21292543978042a81
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2726499Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73092}

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

@@ -35,11 +35,19 @@ using cppgc::internal::HeapObjectHeader;
 class EmbedderNode : public v8::EmbedderGraph::Node {
  public:
   explicit EmbedderNode(const char* name, size_t size)
-      : name_(name), size_(size) {}
+      : name_(name), size_(size) {
+    USE(size_);
+  }
   ~EmbedderNode() override = default;
 
   const char* Name() final { return name_; }
-  size_t SizeInBytes() final { return size_; }
+  size_t SizeInBytes() final {
+#if CPPGC_SUPPORTS_OBJECT_NAMES
+    return size_;
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+    return 0;
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
+  }
 
   void SetWrapperNode(v8::EmbedderGraph::Node* wrapper_node) {
     wrapper_node_ = wrapper_node;

test/unittests/heap/unified-heap-snapshot-unittest.cc

@@ -384,14 +384,21 @@ TEST_F(UnifiedHeapSnapshotTest, MergedWrapperNode) {
           // GCedWithJSRef is merged into MergedObject, replacing its name.
           "NextObject"  // NOLINT
       }));
+  const size_t js_size = Utils::OpenHandle(*wrapper_object)->Size();
+#if CPPGC_SUPPORTS_OBJECT_NAMES
   const size_t cpp_size =
       cppgc::internal::HeapObjectHeader::FromPayload(gc_w_js_ref.Get())
           .GetSize();
-  const size_t js_size = Utils::OpenHandle(*wrapper_object)->Size();
   ForEachEntryWithName(snapshot, GetExpectedName<GCedWithJSRef>(),
                        [cpp_size, js_size](const HeapEntry& entry) {
                          EXPECT_EQ(cpp_size + js_size, entry.self_size());
                        });
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+  ForEachEntryWithName(snapshot, GetExpectedName<GCedWithJSRef>(),
+                       [js_size](const HeapEntry& entry) {
+                         EXPECT_EQ(js_size, entry.self_size());
+                       });
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
 }
 
 namespace {