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

Source/platform/audio/AudioSourceProviderClient.h

Index: Source/platform/audio/AudioSourceProviderClient.h
diff --git a/Source/platform/audio/AudioSourceProviderClient.h b/Source/platform/audio/AudioSourceProviderClient.h
index 28489e0e6119531792b38d016ca42c089dfd9bef..791897928e047c2806b964665140fdfc20767c41 100644
--- a/Source/platform/audio/AudioSourceProviderClient.h
+++ b/Source/platform/audio/AudioSourceProviderClient.h
@@ -30,6 +30,8 @@ namespace WebCore {
 class AudioSourceProviderClient {
 public:
     virtual void setFormat(size_t numberOfChannels, float sampleRate) = 0;
+    virtual void lock() { };
+    virtual void unlock() { };
 protected:
     virtual ~AudioSourceProviderClient() { }
 };