Add missing passive discovery flag

MediaProjectionManagerService had an active media callback which
was causing a service to be bound 100% of the time.  Adding a
passive flag makes it only observe events, and allow the service
to only be bound when needed by apps requesting active discovery.

Bug: 18042409
Bug: 17969854
Change-Id: I1bfa6609e2aa507ee2ce227de50f0e5ae951e000

services/core/java/com/android/server/media/projection/MediaProjectionManagerService.java

@@ -91,7 +91,8 @@ public final class MediaProjectionManagerService extends SystemService
     public void onStart() {
         publishBinderService(Context.MEDIA_PROJECTION_SERVICE, new BinderService(),
                 false /*allowIsolated*/);
-        mMediaRouter.addCallback(MediaRouter.ROUTE_TYPE_REMOTE_DISPLAY, mMediaRouterCallback);
+        mMediaRouter.addCallback(MediaRouter.ROUTE_TYPE_REMOTE_DISPLAY, mMediaRouterCallback,
+                MediaRouter.CALLBACK_FLAG_PASSIVE_DISCOVERY);
     }
 
     @Override