Move audio focus control from media/ to content/ and make it per WebContents.

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

Index: content/public/android/java/src/org/chromium/content/browser/MediaSession.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/MediaSession.java b/content/public/android/java/src/org/chromium/content/browser/MediaSession.java
new file mode 100644
index 0000000000000000000000000000000000000000..7395f9ba2bbbbd525721a55596f60fbc37298eae
--- /dev/null
+++ b/content/public/android/java/src/org/chromium/content/browser/MediaSession.java
@@ -0,0 +1,88 @@
+// 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.CalledByNative;
+import org.chromium.base.JNINamespace;
+import org.chromium.base.Log;
+
+/**
+ * MediaSession is the Java counterpart of content::MediaSession.
+ * It is being used to communicate from content::MediaSession (C++) to the
+ * Android system. A MediaSession is implementing OnAudioFocusChangeListener,
+ * making it an audio focus holder for Android. Thus two instances of
+ * MediaSession can't have audio focus at the same time.
+ * A MediaSession will use the type requested from its C++ counterpart and will
+ * resume its play using the same type if it were to happen, for example, when
+ * it got temporarily suspended by a transient sound like a notification.
+ */
+@JNINamespace("content")
+public class MediaSession implements AudioManager.OnAudioFocusChangeListener {
+    private static final String TAG = "MediaSession";
+
+    private Context mContext;
+    private int mFocusType;
+
+    // Native pointer to C++ content::MediaSession.
+    private final long mNativeMediaSession;
+
+    private MediaSession(final Context context, long nativeMediaSession) {
+        mContext = context;
+        mNativeMediaSession = nativeMediaSession;
+    }
+
+    @CalledByNative
+    private static MediaSession createMediaSession(Context context, long nativeMediaSession) {
+        return new MediaSession(context, nativeMediaSession);
+    }
+
+    @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) {
+        switch (focusChange) {
+            case AudioManager.AUDIOFOCUS_GAIN:
+                if (requestAudioFocusInternal()) {
+                    nativeOnResume(mNativeMediaSession);
+                }
+                break;
+            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
+            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
+                nativeOnSuspend(mNativeMediaSession, true);
+                break;
+            case AudioManager.AUDIOFOCUS_LOSS:
+                abandonAudioFocus();
+                nativeOnSuspend(mNativeMediaSession, false);
+                break;
+            default:
+                Log.w(TAG, "onAudioFocusChange called with unexpected value " + focusChange);
+                break;
+        }
+    }
+
+    private native void nativeOnSuspend(long nativeMediaSession, boolean temporary);
+    private native void nativeOnResume(long nativeMediaSession);
+}