Speculative fix to service not calling startForeground before shutdown

Calling stopForeground should reset the fgRequired bit. Hopefully this fixes
the crash, which checks whether that big is true when calling stopSelf()

BUG=826998

Change-Id: Ib2dee1c5d87f406d4755b924c755697588010658
Reviewed-on: https://chromium-review.googlesource.com/1125080Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572335}

chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java

@@ -354,6 +354,8 @@ public class MediaNotificationManager {
 
         @VisibleForTesting
         void stopListenerService() {
+            // Call stopForeground to guarantee  Android unset the foreground bit.
+            stopForeground(true /* removeNotification */);
             stopSelf();
         }