Fix Java weak reference nullification in MediaSessionAndroid

content/browser/media/session/media_session_android.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/media/session/media_session_android.h"
 
 #include <algorithm>
 #include "content/browser/media/session/media_session_impl.h"
 #include "content/browser/web_contents/web_contents_android.h"
 #include "content/browser/web_contents/web_contents_impl.h"
@@ skipping 45 matching lines @@
     return ScopedJavaLocalRef<jobject>();
 
   MediaSessionImpl* session = MediaSessionImpl::Get(contents);
   DCHECK(session);
   return MediaSessionAndroid::JavaObjectGetter::GetJavaObject(
       session->session_android());
 }
 
 void MediaSessionAndroid::MediaSessionDestroyed() {
   ScopedJavaLocalRef<jobject> j_local_session = GetJavaObject();
-  if (j_local_session.is_null())
+  if (j_local_session.is_null()) {
+    // If the Java MediaSession is already garbage collected, unset the weak
+    // Java reference.
+    j_media_session_.reset();
     return;
+  }
 
   JNIEnv* env = base::android::AttachCurrentThread();
   // The Java object will tear down after this call.
   Java_MediaSessionImpl_mediaSessionDestroyed(env, j_local_session);
   j_media_session_.reset();
 
   WebContentsAndroid* contents_android = GetWebContentsAndroid();
   if (contents_android)
     contents_android->SetMediaSession(nullptr);
 }
@@ skipping 59 matching lines @@
     return nullptr;
   return contents->GetWebContentsAndroid();
 }
 
 ScopedJavaLocalRef<jobject> MediaSessionAndroid::GetJavaObject() {
   JNIEnv* env = base::android::AttachCurrentThread();
   return j_media_session_.get(env);
 }
 
 }  // namespace content