Update ObjectToString to Harmony-draft algorithm

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 0c78b5f27058f923fc02ccd2b9b6dc6e53c8bca7..64720a2f194061ebf70df678e308130bc715acb1 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -3370,6 +3370,37 @@ Local<Array> v8::Object::GetOwnPropertyNames() {
 }
 
 
+static bool GetPredefinedToString(
+    i::Handle<i::String> tag, Local<String>* result) {
+  i::Isolate* i_isolate = tag->GetIsolate();
+  Isolate* isolate = reinterpret_cast<Isolate*>(i_isolate);
+  i::Factory* factory = i_isolate->factory();
+
+  if (i::String::Equals(tag, factory->Arguments_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Arguments]");
+  } else if (i::String::Equals(tag, factory->Array_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Array]");
+  } else if (i::String::Equals(tag, factory->Boolean_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Boolean]");
+  } else if (i::String::Equals(tag, factory->Date_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Date]");
+  } else if (i::String::Equals(tag, factory->Error_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Error]");
+  } else if (i::String::Equals(tag, factory->Function_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Function]");
+  } else if (i::String::Equals(tag, factory->Number_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~Number]");
+  } else if (i::String::Equals(tag, factory->RegExp_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~RegExp]");
+  } else if (i::String::Equals(tag, factory->String_string())) {
+    *result = v8::String::NewFromUtf8(isolate, "[object ~String]");
+  } else {
+    return false;
+  }
+  return true;
+}
+
+
 Local<String> v8::Object::ObjectProtoToString() {
   i::Isolate* i_isolate = Utils::OpenHandle(this)->GetIsolate();
   Isolate* isolate = reinterpret_cast<Isolate*>(i_isolate);
@@ -3379,6 +3410,7 @@ Local<String> v8::Object::ObjectProtoToString() {
   i::Handle<i::JSObject> self = Utils::OpenHandle(this);
 
   i::Handle<i::Object> name(self->class_name(), i_isolate);
+  i::Handle<i::Object> tag;
 
   // Native implementation of Object.prototype.toString (v8natives.js):
   //   var c = %_ClassOf(this);
@@ -3393,6 +3425,27 @@ Local<String> v8::Object::ObjectProtoToString() {
                           i_isolate->factory()->Arguments_string())) {
       return v8::String::NewFromUtf8(isolate, "[object Object]");
     } else {
+      if (internal::FLAG_harmony_tostring) {
+        i::Handle<i::Symbol> toStringTag = Utils::OpenHandle(
+            *Symbol::GetToStringTag(isolate));
+        EXCEPTION_PREAMBLE(i_isolate);
+        has_pending_exception = !i::Runtime::GetObjectProperty(
+            i_isolate, self, toStringTag).ToHandle(&tag);
+        EXCEPTION_BAILOUT_CHECK(i_isolate, Local<v8::String>());
+
+        if (!tag->IsUndefined()) {
+          if (!tag->IsString())
+            return v8::String::NewFromUtf8(isolate, "[object ???]");
+          i::Handle<i::String> tag_name = i::Handle<i::String>::cast(tag);
+          if (!i::String::Equals(class_name, tag_name)) {
+            Local<String> result;
+            if (GetPredefinedToString(tag_name, &result))
+              return result;
+
+            class_name = tag_name;
+          }
+        }
+      }
       const char* prefix = "[object ";
       Local<String> str = Utils::ToLocal(class_name);
       const char* postfix = "]";
@@ -6199,6 +6252,11 @@ Local<Symbol> v8::Symbol::GetUnscopables(Isolate* isolate) {
 }
 
 
+Local<Symbol> v8::Symbol::GetToStringTag(Isolate* isolate) {
+  return GetWellKnownSymbol(isolate, "Symbol.toStringTag");
+}
+
+
 Local<Private> v8::Private::New(Isolate* isolate, Local<String> name) {
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
   LOG_API(i_isolate, "Private::New()");