Supports "class string" based on @@toStringTag.

third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp b/third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp
index 6399a5b5f905e718c0ff2e5b7ebd55c4dca60163..380e9409b55660dcb30ec4599a76c52d700b2988 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp
@@ -313,6 +313,12 @@ v8::Local<v8::Signature> V8DOMConfiguration::installDOMClassTemplate(v8::Isolate
     v8::Local<v8::ObjectTemplate> instanceTemplate = functionDescriptor->InstanceTemplate();
     v8::Local<v8::ObjectTemplate> prototypeTemplate = functionDescriptor->PrototypeTemplate();
     instanceTemplate->SetInternalFieldCount(fieldCount);
+    // TODO(yukishiino): We should set the class string to the platform object
+    // (|instanceTemplate|), too.  The reason that we don't set it is that

[adamk, 2016/02/12 18:31:33]

Can you say more about exactly what this patch does in the CL description? It
refers to the WebIDL spec, but since you're not setting the property on the
instances, we don't match the spec directly. See the bug caitp links to for more
discussion of the issues at hand; there's more at stake than just the
minor-dom-gc layout test.

+    // it prevents minor GC to collect unreachable DOM objects (a layout test
+    // fast/dom/minor-dom-gc.html fails if we set the class string).
+    // See also http://heycam.github.io/webidl/#es-platform-objects

[caitp (gmail), 2016/02/12 14:44:46]

Has there been more discussion about this since
https://www.w3.org/Bugs/Public/show_bug.cgi?id=28244 ?

+    setClassString(isolate, prototypeTemplate, interfaceName);
     if (!parentClass.IsEmpty()) {
         functionDescriptor->Inherit(parentClass);
         // Marks the prototype object as one of native-backed objects.
@@ -345,4 +351,9 @@ v8::Local<v8::FunctionTemplate> V8DOMConfiguration::domClassTemplate(v8::Isolate
     return result;
 }
 
+void V8DOMConfiguration::setClassString(v8::Isolate* isolate, v8::Local<v8::ObjectTemplate> objectTemplate, const char* classString)
+{
+    objectTemplate->Set(v8::Symbol::GetToStringTag(isolate), v8AtomicString(isolate, classString), static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontEnum));
+}
+
 } // namespace blink