Introduce AudioSourceProviderClientLockScope.

Source/modules/webaudio/MediaElementAudioSourceNode.cpp

 /*
  * 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 129 matching lines @@
             outputBus->zero();
         }
     } else {
         // We failed to acquire the lock.
         outputBus->zero();
     }
 }
 
 void MediaElementAudioSourceNode::lock()
 {
-    m_keepAliveWhileLocking = this;
+#if !ENABLE(OILPAN)
+    ref();
+#endif
     m_processLock.lock();
 }
 
 void MediaElementAudioSourceNode::unlock()
 {
     m_processLock.unlock();
-    m_keepAliveWhileLocking.clear();
+#if !ENABLE(OILPAN)
+    deref();
+#endif
 }
 
 void MediaElementAudioSourceNode::trace(Visitor* visitor)
 {
     visitor->trace(m_mediaElement);
     AudioSourceNode::trace(visitor);
     AudioSourceProviderClient::trace(visitor);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)