Check caller for sending media key to global priority session

am: d409d18686

Change-Id: I533ac492152a3aee906d3bf09df9dd965e1213bf

services/core/java/com/android/server/media/MediaSessionService.java

@@ -767,6 +767,13 @@ public class MediaSessionService extends SystemService implements Monitor {
                             + "setup is in progress.");
                     return;
                 }
+                if (isGlobalPriorityActive() && uid != Process.SYSTEM_UID) {
+                    // Prevent dispatching key event through reflection while the global priority
+                    // session is active.
+                    Slog.i(TAG, "Only the system can dispatch media key event "
+                            + "to the global priority session.");
+                    return;
+                }
 
                 synchronized (mLock) {
                     // If we don't have a media button receiver to fall back on