Allow objects with "" properties to stay fast.

src/runtime.h

 // 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 267 matching lines @@
   /* Eval */ \
   F(GlobalReceiver, 1, 1) \
   F(IsAttachedGlobal, 1, 1) \
   F(ResolvePossiblyDirectEval, 5, 2) \
   \
   F(SetProperty, -1 /* 4 or 5 */, 1) \
   F(DefineOrRedefineDataProperty, 4, 1) \
   F(DefineOrRedefineAccessorProperty, 5, 1) \
   F(IgnoreAttributesAndSetProperty, -1 /* 3 or 4 */, 1) \
   F(GetDataProperty, 2, 1) \
+  F(SetHiddenProperty, 3, 1) \
   \
   /* Arrays */ \
   F(RemoveArrayHoles, 2, 1) \
   F(GetArrayKeys, 2, 1) \
   F(MoveArrayContents, 2, 1) \
   F(EstimateNumberOfElements, 1, 1) \
   F(ArrayConstructor, -1, 1) \
   F(InternalArrayConstructor, -1, 1) \
   \
   /* Getters and Setters */ \
@@ skipping 575 matching lines @@
 class AllocateDoubleAlignFlag:    public BitField<bool,            0, 1> {};
 class AllocateTargetSpace:        public BitField<AllocationSpace, 1, 3> {};
 
 class DeclareGlobalsEvalFlag:     public BitField<bool,         0, 1> {};
 class DeclareGlobalsNativeFlag:   public BitField<bool,         1, 1> {};
 class DeclareGlobalsLanguageMode: public BitField<LanguageMode, 2, 2> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_