Move many calls of lazyInitialize() from AudioContext to AudioNode.

Source/modules/webaudio/AudioContext.h

Index: Source/modules/webaudio/AudioContext.h
diff --git a/Source/modules/webaudio/AudioContext.h b/Source/modules/webaudio/AudioContext.h
index 5fe579dfa8adf1334405816f859f0b20c6dfdb90..49f02cc935ae0e1ef60b61680197976da36c0ea7 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -85,6 +85,8 @@ public:
     virtual ~AudioContext();
 
     bool isInitialized() const;
+    // This is called on constructor of AudioNode when the first node of context is created except destination node.

[Raymond Toy, 2014/04/02 17:11:32]

I think this comment is slightly wrong because the destination node is an
AudioNode.  When the destination node is created the AudioNode constructor is
called, but since m_destinationNode isn't set yet, nothing happens.

Maybe the following is better?
// The constructor of an AudioNode must call this to initialize the context.

[KhNo, 2014/04/03 13:21:02]

Done.

+    void lazyInitialize();
 
     bool isOfflineContext() { return m_isOfflineContext; }
 
@@ -245,7 +247,6 @@ protected:
 private:
     void constructCommon();
 
-    void lazyInitialize();
     void uninitialize();
 
     // ExecutionContext calls stop twice.