Remove modules/webaudio/MediaElementAudioSourceNode.h dependency from core.

Source/modules/webaudio/MediaElementAudioSourceNode.h

Index: Source/modules/webaudio/MediaElementAudioSourceNode.h
diff --git a/Source/modules/webaudio/MediaElementAudioSourceNode.h b/Source/modules/webaudio/MediaElementAudioSourceNode.h
index df4e90fac696d7ce162a341288b8002a813f0f54..292794e591dfe961dfc9540b4a1e9f350f367367 100644
--- a/Source/modules/webaudio/MediaElementAudioSourceNode.h
+++ b/Source/modules/webaudio/MediaElementAudioSourceNode.h
@@ -53,8 +53,8 @@ public:
     // AudioSourceProviderClient
     virtual void setFormat(size_t numberOfChannels, float sampleRate) OVERRIDE;
 
-    void lock();
-    void unlock();
+    virtual void lock() OVERRIDE;
+    virtual void unlock() OVERRIDE;
 
 private:
     MediaElementAudioSourceNode(AudioContext*, HTMLMediaElement*);