Add support for [TreatNullAs] extended attribute for reflected attributes

Source/core/html/HTMLMediaElement.idl

 /*
  * Copyright (C) 2007, 2010, 2011, 2012 Apple 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 14 matching lines @@
 
 [
     EnabledAtRuntime=Media,
     ActiveDOMObject
 ] interface HTMLMediaElement : HTMLElement {
 
 // error state
 readonly attribute MediaError error;
 
 // network state
-[Reflect, URL] attribute DOMString src;
+[Reflect, TreatNullAs=NullString, URL] attribute DOMString src;
 [URL] readonly attribute DOMString currentSrc;
 
 const unsigned short NETWORK_EMPTY = 0;
 const unsigned short NETWORK_IDLE = 1;
 const unsigned short NETWORK_LOADING = 2;
 const unsigned short NETWORK_NO_SOURCE = 3;
 readonly attribute unsigned short networkState;
 attribute DOMString preload;
 
 readonly attribute TimeRanges buffered;
@@ skipping 49 matching lines @@
 [EnabledAtRuntime=PrefixedEncryptedMedia] attribute EventHandler onwebkitkeyadded;
 [EnabledAtRuntime=PrefixedEncryptedMedia] attribute EventHandler onwebkitkeyerror;
 [EnabledAtRuntime=PrefixedEncryptedMedia] attribute EventHandler onwebkitkeymessage;
 [EnabledAtRuntime=PrefixedEncryptedMedia] attribute EventHandler onwebkitneedkey;
 
 [EnabledAtRuntime=EncryptedMedia, Conditional=ENCRYPTED_MEDIA_V2] attribute MediaKeys mediaKeys;
 
 [EnabledAtRuntime=VideoTrack, RaisesException] TextTrack addTextTrack(DOMString kind, optional DOMString label, optional DOMString language);
 [EnabledAtRuntime=VideoTrack] readonly attribute TextTrackList textTracks;
 
-[Reflect, TreatNullAs=NullString] attribute DOMString mediaGroup;
+[Reflect, TreatNullAs=NullString, TreatNullAs=NullString] attribute DOMString mediaGroup;
 [CustomSetter] attribute MediaController controller;
 };