Combine MediaSession Callback and TransportControlsCallback

This combines them into a single Callback class and adds default
handling to media buttons to check the available actions and call
one of the other methods if appropriate.

Change-Id: If9897d8cf6d8d8046aa85a646c22382f1db1461b

media/java/android/media/RemoteControlClient.java

@@ -970,8 +970,7 @@ import java.lang.IllegalArgumentException;
     public final static int RCSE_ID_UNREGISTERED = -1;
 
     // USE_SESSIONS
-    private MediaSession.TransportControlsCallback mTransportListener
-            = new MediaSession.TransportControlsCallback() {
+    private MediaSession.Callback mTransportListener = new MediaSession.Callback() {
 
         @Override
         public void onSeekTo(long pos) {