WebAudio: Remove AudioNode::RefType.

Source/modules/webaudio/AudioNodeOutput.h

 /*
  * Copyright (C) 2010, 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 116 matching lines @@
     // The main thread sets m_desiredNumberOfChannels which will later get picked up in the audio thread in updateNumberOfChannels().
     unsigned m_numberOfChannels;
     unsigned m_desiredNumberOfChannels;
 
     // m_internalBus and m_inPlaceBus must only be changed in the audio thread with the context's graph lock (or constructor).
     RefPtr<AudioBus> m_internalBus;
     RefPtr<AudioBus> m_inPlaceBus;
     // If m_isInPlace is true, use m_inPlaceBus as the valid AudioBus; If false, use the default m_internalBus.
     bool m_isInPlace;
 
-    HashSet<AudioNodeInput*> m_inputs;
-    typedef HashSet<AudioNodeInput*>::iterator InputsIterator;
+    // This RefPtr<AudioNode> is connection reference. We must call AudioNode::
+    // makeConnection() after ref(), and call AudioNode::breakConnection()
+    // before deref().
+    HashMap<AudioNodeInput*, RefPtr<AudioNode> > m_inputs;
+    typedef HashMap<AudioNodeInput*, RefPtr<AudioNode> >::iterator InputsIterator;
     bool m_isEnabled;
 
     // For the purposes of rendering, keeps track of the number of inputs and AudioParams we're connected to.
     // These value should only be changed at the very start or end of the rendering quantum.
     unsigned m_renderingFanOutCount;
     unsigned m_renderingParamFanOutCount;
 
     WillBePersistentHeapHashSet<RefPtrWillBeMember<AudioParam> > m_params;
 };
 
 } // namespace WebCore
 
 #endif // AudioNodeOutput_h