Introduce AudioSourceProviderClientLockScope.

Source/modules/webaudio/MediaElementAudioSourceNode.h

 /*
  * Copyright (C) 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:
  * 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 55 matching lines @@
     // As an audio source, we will never propagate silence.
     virtual bool propagatesSilence() const OVERRIDE { return false; }
 
     RefPtrWillBeMember<HTMLMediaElement> m_mediaElement;
     Mutex m_processLock;
 
     unsigned m_sourceNumberOfChannels;
     double m_sourceSampleRate;
 
     OwnPtr<MultiChannelResampler> m_multiChannelResampler;
-    // Oilpan: This object must be alive between lock() and unlock().
-    GC_PLUGIN_IGNORE("http://crbug.com/395940")
-    RefPtrWillBePersistent<MediaElementAudioSourceNode> m_keepAliveWhileLocking;
 };
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)
 
 #endif // MediaElementAudioSourceNode_h