Support for multiple VideoCall.Listeners for a VideoCall.

The current code assumes that only a single instance of VideoCall will be
provided to the default system InCall UI.  Ideally multiple
InCallService implementations should be able to use the VideoCall APIs.
Note: it only really makes sense for a single InCallService to get/set
the video surfaces.

- Fixed bug in ParcelableCall which would cause a new instance of
VideoCallImpl to be created every time a call is updated from Telecom.
Added a flag to ParcelableCall to indicate whether the parcel includes a
change to the video provider information, which is used when unparceling
to determine whether to set/create the video call impl.
- Renamed "setVideoCallback" to "addVideocallback".
- Modified Connection.VideoProvider code to keep a list of Video callbacks
and fire off all of them when Video Provider changes occur.

Bug: 20092420
Change-Id: Ic16b6afe1b7532cc64d006c133adbae57946d97d

telecomm/java/android/telecom/InCallService.java

@@ -212,6 +212,11 @@ public abstract class InCallService extends Service {
          */
         public abstract void setVideoCallListener(VideoCall.Listener videoCallListener);
 
+        /**
+         * Clears the video call listener set via {@link #setVideoCallListener(Listener)}.
+         */
+        public abstract void removeVideoCallListener();
+
         /**
          * Sets the camera to be used for video recording in a video call.
          *