WebAudio: Remove AudioNode::RefType.

Source/modules/webaudio/AudioNodeOutput.h

Index: Source/modules/webaudio/AudioNodeOutput.h
diff --git a/Source/modules/webaudio/AudioNodeOutput.h b/Source/modules/webaudio/AudioNodeOutput.h
index ade9c1c3350dbced00ad39f28ee870d246e7d95e..f63d108e6ea5ca3630998a17e3196fd7db34ed6e 100644
--- a/Source/modules/webaudio/AudioNodeOutput.h
+++ b/Source/modules/webaudio/AudioNodeOutput.h
@@ -136,6 +136,11 @@ private:
 
     HashSet<AudioNodeInput*> m_inputs;
     typedef HashSet<AudioNodeInput*>::iterator InputsIterator;
+    // The content of m_inputNodes must be synchronized with m_inputs.
+    // This RefPtr is connection reference. We must call AudioNode::
+    // makeConnection() after ref(), and call AudioNode::breakConnection()
+    // before deref().
+    HashSet<RefPtr<AudioNode> > m_inputNodes;

[tkent, 2014/07/14 03:56:04]

Using HashSet<> was wrong.  We can associate an AudioNodeOutput to multiple
AudioNodeInputs for single AudioNode.
I'm changing m_inputs type from HashSet<AudioNodeInput*> to
HashMap<AudioNodeInput*, RefPtr<AudioNode>>.

     bool m_isEnabled;
 
     // For the purposes of rendering, keeps track of the number of inputs and AudioParams we're connected to.