Allow users of the V8 API to distinguish between unset and undefined HiddenValues

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 8ca858dca91d367e5ba9bb849c8a22ec3f673a1d..014d82ee4f0aab86c5f16ca339c22b335c42753b 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -3935,7 +3935,7 @@ v8::Local<v8::Value> v8::Object::GetHiddenValue(v8::Handle<v8::String> key) {
   i::Handle<i::String> key_string =
       isolate->factory()->InternalizeString(key_obj);
   i::Handle<i::Object> result(self->GetHiddenProperty(*key_string), isolate);
-  if (result->IsUndefined()) return v8::Local<v8::Value>();
+  if (result->IsTheHole()) return v8::Local<v8::Value>();
   return Utils::ToLocal(result);
 }