Allow objects with "" properties to stay fast.

src/stub-cache.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 161 matching lines @@
                                                Handle<HeapType> type) {
   InlineCacheHolderFlag flag = IC::GetCodeCacheFlag(*type);
   Handle<Map> stub_holder = IC::GetCodeCacheHolder(flag, *type, isolate());
   // If no dictionary mode objects are present in the prototype chain, the load
   // nonexistent IC stub can be shared for all names for a given map and we use
   // the empty string for the map cache in that case. If there are dictionary
   // mode objects involved, we need to do negative lookups in the stub and
   // therefore the stub will be specific to the name.
   Handle<Map> current_map = stub_holder;
   Handle<Name> cache_name = current_map->is_dictionary_map()
-      ? name : Handle<Name>::cast(isolate()->factory()->empty_string());
+      ? name : Handle<Name>::cast(isolate()->factory()->nonexistent_symbol());
   Handle<Object> next(current_map->prototype(), isolate());
   Handle<JSObject> last = Handle<JSObject>::null();
   while (!next->IsNull()) {
     last = Handle<JSObject>::cast(next);
     next = handle(current_map->prototype(), isolate());
     current_map = handle(Handle<HeapObject>::cast(next)->map());
     if (current_map->is_dictionary_map()) cache_name = name;
   }
 
   // Compile the stub that is either shared for all names or
@@ skipping 1269 matching lines @@
           Handle<FunctionTemplateInfo>(
               FunctionTemplateInfo::cast(signature->receiver()));
     }
   }
 
   is_simple_api_call_ = true;
 }
 
 
 } }  // namespace v8::internal