IDL: Add support for [TreatNullAs=EmptyString]

Source/bindings/core/v8/custom/V8CSSStyleDeclarationCustom.cpp

 /*
  * Copyright (C) 2007-2011 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 201 matching lines @@
     v8SetReturnValueString(info, result, info.GetIsolate());
 }
 
 void V8CSSStyleDeclaration::namedPropertySetterCustom(v8::Local<v8::String> name, v8::Local<v8::Value> value, const v8::PropertyCallbackInfo<v8::Value>& info)
 {
     CSSStyleDeclaration* impl = V8CSSStyleDeclaration::toNative(info.Holder());
     CSSPropertyInfo* propInfo = cssPropertyInfo(name);
     if (!propInfo)
         return;
 
-    TOSTRING_VOID(V8StringResource<WithNullCheck>, propertyValue, value);
+    TOSTRING_VOID(V8StringResource<TreatNullAsNullString>, propertyValue, value);
     ExceptionState exceptionState(ExceptionState::SetterContext, getPropertyName(static_cast<CSSPropertyID>(propInfo->propID)), "CSSStyleDeclaration", info.Holder(), info.GetIsolate());
     impl->setPropertyInternal(static_cast<CSSPropertyID>(propInfo->propID), propertyValue, false, exceptionState);
 
     if (exceptionState.throwIfNeeded())
         return;
 
     v8SetReturnValue(info, value);
 }
 
 } // namespace WebCore