Don't forward media keys to the app if the phone session is active

This checks if the phone app is currently getting or in a call when a
media key event is sent and sends it to the phone session instead of the
foreground app if it is.

bug:17527302
Change-Id: Ie5d6cf0c897da81d106f2b1a0561b79f4fc35e82
diff --git a/services/core/java/com/android/server/media/MediaSessionService.java b/services/core/java/com/android/server/media/MediaSessionService.java
index aaa29fc..02c9fcb5 100644
--- a/services/core/java/com/android/server/media/MediaSessionService.java
+++ b/services/core/java/com/android/server/media/MediaSessionService.java
@@ -743,6 +743,11 @@
         }
 
         @Override
+        public boolean isGlobalPriorityActive() {
+            return mPriorityStack.isGlobalPriorityActive();
+        }
+
+        @Override
         public void dump(FileDescriptor fd, final PrintWriter pw, String[] args) {
             if (getContext().checkCallingOrSelfPermission(Manifest.permission.DUMP)
                     != PackageManager.PERMISSION_GRANTED) {