IDL: Support argument default values

Source/bindings/v8/V8StringResource.h

 /*
  * Copyright (C) 2009 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 172 matching lines @@
     void operator=(v8::Handle<v8::Value> object)
     {
         m_v8Object = object;
     }
 
     void operator=(const String& string)
     {
         setString(string);
     }
 
+    void operator=(std::nullptr_t)
+    {
+        setString(String());
+    }
+
     bool prepare()
     {
         if (m_v8Object.IsEmpty())
             return true;
 
         if (!isValid()) {
             setString(String());
             return true;
         }
 
@@ skipping 52 matching lines @@
 }
 
 template<> inline bool V8StringResource<WithUndefinedOrNullCheck>::isValid() const
 {
     return !m_v8Object->IsNull() && !m_v8Object->IsUndefined();
 }
 
 } // namespace WebCore
 
 #endif // V8StringResource_h