Implement sealing, freezing, and related functions for proxies.

src/objects.h

 // Copyright 2011 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 6457 matching lines @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalPropertyCell);
 };
 
 
 // The JSProxy describes EcmaScript Harmony proxies
 class JSProxy: public JSReceiver {
  public:
   // [handler]: The handler property.
   DECL_ACCESSORS(handler, Object)
 
+  // [padding]: The padding slot (unused, see below).
+  DECL_ACCESSORS(padding, Object)
+
   // Casting.
   static inline JSProxy* cast(Object* obj);
 
   MUST_USE_RESULT MaybeObject* SetPropertyWithHandler(
       String* name,
       Object* value,
       PropertyAttributes attributes,
       StrictModeFlag strict_mode);
 
   MUST_USE_RESULT MaybeObject* DeletePropertyWithHandler(
       String* name,
       DeleteMode mode);
 
   MUST_USE_RESULT PropertyAttributes GetPropertyAttributeWithHandler(
       JSReceiver* receiver,
       String* name,
       bool* has_exception);
 
+  // Turn this into an (empty) JSObject.
+  void Fix();
+
   // Dispatched behavior.
 #ifdef OBJECT_PRINT
   inline void JSProxyPrint() {
     JSProxyPrint(stdout);
   }
   void JSProxyPrint(FILE* out);
 #endif
 #ifdef DEBUG
   void JSProxyVerify();
 #endif
 
-  // Layout description.
+  // Layout description. We add padding so that a proxy has the same
+  // size as a virgin JSObject. This is essential for becoming a JSObject
+  // upon freeze.
   static const int kHandlerOffset = HeapObject::kHeaderSize;
-  static const int kSize = kHandlerOffset + kPointerSize;
+  static const int kPaddingOffset = kHandlerOffset + kPointerSize;
+  static const int kSize = kPaddingOffset + kPointerSize;
+
+  STATIC_CHECK(kSize == JSObject::kHeaderSize);
 
   typedef FixedBodyDescriptor<kHandlerOffset,
                               kHandlerOffset + kPointerSize,
                               kSize> BodyDescriptor;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSProxy);
 };
 
 
@@ skipping 644 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_