Prevent false positive from GCMole in DeferredFormatStackTrace.

R=yangguo@chromium.org
TEST=gcmole

Review URL: https://codereview.chromium.org/14416010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14447 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -7705,7 +7705,8 @@ void ErrorObjectList::DeferredFormatStackTrace(Isolate* isolate) {
       if (!getter_obj->IsJSFunction()) continue;
       getter_fun = JSFunction::cast(getter_obj);
       String* key = isolate->heap()->hidden_stack_trace_string();
-      if (key != getter_fun->GetHiddenProperty(key)) continue;
+      Object* value = getter_fun->GetHiddenProperty(key);
+      if (key != value) continue;
     }
 
     budget--;