Fix for MediaSessionObserver.stopObserving

content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java

Index: content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
diff --git a/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java b/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
index fd789ded767928340da05c3081a929b24a390bbf..5e03463b9a29bbf9a5226e19632270544cd57a23 100644
--- a/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
+++ b/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
@@ -62,5 +62,6 @@ public abstract class MediaSessionObserver {
     public final void stopObserving() {
         if (mMediaSession == null) return;
         mMediaSession.removeObserver(this);
+        mMediaSession = null;
     }
 }