Make sure getAttribute() / setAttribute() callers use AtomicStrings

Source/core/html/track/TextTrack.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2011, 2012, 2013 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
@@ skipping 46 matching lines @@
 public:
     static PassRefPtr<TextTrack> create(Document& document, TextTrackClient* client, const AtomicString& kind, const AtomicString& label, const AtomicString& language)
     {
         return adoptRef(new TextTrack(document, client, kind, label, language, emptyAtom, AddTrack));
     }
     virtual ~TextTrack();
 
     void setMediaElement(HTMLMediaElement* element) { m_mediaElement = element; }
     HTMLMediaElement* mediaElement() { return m_mediaElement; }
 
-    AtomicString kind() const { return m_kind; }
+    const AtomicString& kind() const { return m_kind; }
     void setKind(const AtomicString&);
 
     static const AtomicString& subtitlesKeyword();
     static const AtomicString& captionsKeyword();
     static const AtomicString& descriptionsKeyword();
     static const AtomicString& chaptersKeyword();
     static const AtomicString& metadataKeyword();
     static bool isValidKindKeyword(const AtomicString&);
 
     AtomicString label() const { return m_label; }
@@ skipping 81 matching lines @@
     TextTrackType m_trackType;
     ReadinessState m_readinessState;
     int m_trackIndex;
     int m_renderedTrackIndex;
     bool m_hasBeenConfigured;
 };
 
 } // namespace WebCore
 
 #endif