Remove JSReceiver::GetPrototype and replace it with PrototypeIterator calls

src/json-stringifier.h

Index: src/json-stringifier.h
diff --git a/src/json-stringifier.h b/src/json-stringifier.h
index 0a453ef67f6d6404d714cf13e6a29a011014b426..ba4c87ad1d5f14b8b64f99608e3fa4a0d9fc671f 100644
--- a/src/json-stringifier.h
+++ b/src/json-stringifier.h
@@ -631,8 +631,9 @@ BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSObject(
   Result stack_push = StackPush(object);
   if (stack_push != SUCCESS) return stack_push;
   if (object->IsJSGlobalProxy()) {
-    object = Handle<JSObject>(
-                 JSObject::cast(object->GetPrototype()), isolate_);
+    // TODO(verwaest): This will crash if the global proxy is detached.
+    PrototypeIterator iter(isolate_, object);
+    object = Handle<JSObject>::cast(PrototypeIterator::GetCurrent(iter));
     ASSERT(object->IsGlobalObject());
   }