Add a helper for implementing Promise-valued properties.

Source/bindings/core/v8/ScriptPromise.h

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 75 matching lines @@
     bool isEmpty() const
     {
         return m_promise.isEmpty();
     }
 
     void clear()
     {
         m_promise.clear();
     }
 
+    bool operator==(const ScriptPromise& value) const
+    {
+        return m_promise == value.m_promise;
+    }
+
+    bool operator!=(const ScriptPromise& value) const
+    {
+        return !operator==(value);
+    }
+
     // Constructs and returns a ScriptPromise from |value|.
     // if |value| is not a Promise object, returns a Promise object
     // resolved with |value|.
     // Returns |value| itself if it is a Promise.
     static ScriptPromise cast(ScriptState*, const ScriptValue& /*value*/);
     static ScriptPromise cast(ScriptState*, v8::Handle<v8::Value> /*value*/);
 
     static ScriptPromise reject(ScriptState*, const ScriptValue&);
     static ScriptPromise reject(ScriptState*, v8::Handle<v8::Value>);
 
@@ skipping 16 matching lines @@
 
 private:
     RefPtr<ScriptState> m_scriptState;
     ScriptValue m_promise;
 };
 
 } // namespace WebCore
 
 
 #endif // ScriptPromise_h