add interceptors which do not mask existing properties

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 10551 matching lines @@
 class InterceptorInfo: public Struct {
  public:
   DECL_ACCESSORS(getter, Object)
   DECL_ACCESSORS(setter, Object)
   DECL_ACCESSORS(query, Object)
   DECL_ACCESSORS(deleter, Object)
   DECL_ACCESSORS(enumerator, Object)
   DECL_ACCESSORS(data, Object)
   DECL_BOOLEAN_ACCESSORS(can_intercept_symbols)
   DECL_BOOLEAN_ACCESSORS(all_can_read)
+  DECL_BOOLEAN_ACCESSORS(non_masking)
 
   inline int flags() const;
   inline void set_flags(int flags);
 
   DECLARE_CAST(InterceptorInfo)
 
   // Dispatched behavior.
   DECLARE_PRINTER(InterceptorInfo)
   DECLARE_VERIFIER(InterceptorInfo)
 
   static const int kGetterOffset = HeapObject::kHeaderSize;
   static const int kSetterOffset = kGetterOffset + kPointerSize;
   static const int kQueryOffset = kSetterOffset + kPointerSize;
   static const int kDeleterOffset = kQueryOffset + kPointerSize;
   static const int kEnumeratorOffset = kDeleterOffset + kPointerSize;
   static const int kDataOffset = kEnumeratorOffset + kPointerSize;
   static const int kFlagsOffset = kDataOffset + kPointerSize;
   static const int kSize = kFlagsOffset + kPointerSize;
 
   static const int kCanInterceptSymbolsBit = 0;
   static const int kAllCanReadBit = 1;
+  static const int kNonMasking = 2;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(InterceptorInfo);
 };
 
 
 class CallHandlerInfo: public Struct {
  public:
   DECL_ACCESSORS(callback, Object)
   DECL_ACCESSORS(data, Object)
@@ skipping 380 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_