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

Source/core/html/LinkResource.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 50 matching lines @@
 protected:
     HTMLLinkElement* m_owner;
 };
 
 class LinkRequestBuilder {
 public:
     explicit LinkRequestBuilder(HTMLLinkElement* owner);
 
     bool isValid() const { return !m_url.isEmpty() && m_url.isValid(); }
     const KURL& url() const { return m_url; }
-    const String& charset() const { return m_charset; }
+    const AtomicString& charset() const { return m_charset; }
     FetchRequest build(bool blocking) const;
 
 private:
     HTMLLinkElement* m_owner;
     KURL m_url;
-    String m_charset;
+    AtomicString m_charset;
 };
 
 } // namespace WebCore
 
 #endif // LinkResource_h