Fixing MediaSessionDelegateAndroid referencing destroyed MediaSession

content/public/android/java/src/org/chromium/content/browser/MediaSessionDelegate.java

 // Copyright 2015 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.
 
 package org.chromium.content.browser;
 
 import android.content.Context;
 import android.media.AudioManager;
 
 import org.chromium.base.Log;
@@ skipping 16 matching lines @@
     private static final String TAG = "MediaSession";
 
     // These need to match the values in native apps.
     public static final double DUCKING_VOLUME_MULTIPLIER = 0.2f;
     public static final double DEFAULT_VOLUME_MULTIPLIER = 1.0f;
 
     private Context mContext;
     private int mFocusType;
     private boolean mIsDucking = false;
 
-    // Native pointer to C++ content::MediaSessionAndroid.
-    private final long mNativeMediaSessionDelegateAndroid;
+    // Native pointer to C++ content::MediaSessionDelegateAndroid.
+    // It will be set to 0 when the native MediaSessionDelegateAndroid object is destroyed.
+    private long mNativeMediaSessionDelegateAndroid;
 
     private MediaSessionDelegate(final Context context, long nativeMediaSessionDelegateAndroid) {
         mContext = context;
         mNativeMediaSessionDelegateAndroid = nativeMediaSessionDelegateAndroid;
     }
 
     @CalledByNative
     private static MediaSessionDelegate create(Context context,
                                                long nativeMediaSessionDelegateAndroid) {
         return new MediaSessionDelegate(context, nativeMediaSessionDelegateAndroid);
     }
 
     @CalledByNative
     private void tearDown() {
         abandonAudioFocus();
+        mNativeMediaSessionDelegateAndroid = 0;
     }
 
     @CalledByNative
     private boolean requestAudioFocus(boolean transientFocus) {
         mFocusType = transientFocus ? AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK
                 : AudioManager.AUDIOFOCUS_GAIN;
         return requestAudioFocusInternal();
     }
 
     @CalledByNative
     private void abandonAudioFocus() {
         AudioManager am = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
         am.abandonAudioFocus(this);
     }
 
     private boolean requestAudioFocusInternal() {
         AudioManager am = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
 
         int result = am.requestAudioFocus(this, AudioManager.STREAM_MUSIC, mFocusType);
         return result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED;
     }
 
     @Override
     public void onAudioFocusChange(int focusChange) {
+        if (mNativeMediaSessionDelegateAndroid == 0) return;
+
         switch (focusChange) {
             case AudioManager.AUDIOFOCUS_GAIN:
                 if (mIsDucking) {
                     nativeOnSetVolumeMultiplier(mNativeMediaSessionDelegateAndroid,
                                                 DEFAULT_VOLUME_MULTIPLIER);
                     mIsDucking = false;
                 } else {
                     nativeOnResume(mNativeMediaSessionDelegateAndroid);
                 }
                 break;
@@ skipping 15 matching lines @@
                 break;
         }
     }
 
     private native void nativeOnSuspend(long nativeMediaSessionDelegateAndroid, boolean temporary);
     private native void nativeOnResume(long nativeMediaSessionDelegateAndroid);
     private native void nativeOnSetVolumeMultiplier(long nativeMediaSessionDelegateAndroid,
                                                     double volumeMultiplier);
     private native void nativeRecordSessionDuck(long nativeMediaSessionDelegateAndroid);
 }