Cleanup namespace usage from animation to exported in platform/

Source/platform/exported/WebPrerenderingSupport.cpp

 /*
  * Copyright (C) 2012 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 33 matching lines @@
 void WebPrerenderingSupport::shutdown()
 {
     s_platform = 0;
 }
 
 WebPrerenderingSupport* WebPrerenderingSupport::current()
 {
     return s_platform;
 }
 
-}
+} // namespace blink