NOT FOR LANDING Introduce and use WebMediaSession

public/platform/WebMediaSession.h

Index: public/platform/WebMediaSession.h
diff --git a/Source/modules/webaudio/testing/InternalsWebAudio.h b/public/platform/WebMediaSession.h
similarity index 51%
copy from Source/modules/webaudio/testing/InternalsWebAudio.h
copy to public/platform/WebMediaSession.h
index 9536a49d4e3c91189ded00bf8748a900e4100a60..78fe714e0db222659b0837cf82af85f4b3d77112 100644
--- a/Source/modules/webaudio/testing/InternalsWebAudio.h
+++ b/public/platform/WebMediaSession.h
@@ -2,18 +2,19 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef InternalsWebAudio_h
-#define InternalsWebAudio_h
+#ifndef WebMediaSession_h
+#define WebMediaSession_h
 
 namespace blink {
 
-class Internals;
-
-class InternalsWebAudio {
+class WebMediaSession {
 public:
-    static unsigned audioHandlerCount(Internals&);
+    virtual ~WebMediaSession() { }
+
+    virtual void activate() = 0;
+    virtual void deactivate() = 0;
 };
 
 } // namespace blink
 
-#endif // InternalsWebAudio_h
+#endif // WebMediaSession_h