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..bb199ae3d374babe2dc10f3ffc05a07d98bd43e6
--- /dev/null
+++ b/content/public/android/java/src/org/chromium/content/browser/MediaSession.java
@@ -0,0 +1,75 @@
+// 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;
+
+/**
+ * MediaSession is the Java counterpart of content::MediaSession.

[whywhat, 2015/05/12 12:50:46]

I believe more comment is due. E.g. explain the fact that it maintains the
"strongest" audio focus type needed at the moment and keeps the current focus
type acquired in mFocusType.

[mlamouri (slow - plz ping), 2015/05/19 21:56:17]

Done.

+ */
+@JNINamespace("content")
+public class MediaSession implements AudioManager.OnAudioFocusChangeListener {
+
+    private Context mContext;
+    private int mFocusType;
+
+    // Native pointer to C++ content::MediaSession.
+    private long mNativeMediaSession;

[whywhat, 2015/05/12 12:50:46]

make it final.
have you made it certain that the C++ counterpart outlives the Java one (I
believe by holding the Java object in a strong reference)

[mlamouri (slow - plz ping), 2015/05/19 21:56:17]

Yes, the java object is held as ScopedJavaGlobalRef.

+
+    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;
+    }
+
+    public void onAudioFocusChange(int focusChange) {

[whywhat, 2015/05/12 12:50:46]

@Override?

[mlamouri (slow - plz ping), 2015/05/19 21:56:17]

Done.

+        switch (focusChange) {
+            case AudioManager.AUDIOFOCUS_GAIN:
+                if (requestAudioFocusInternal()) {

[whywhat, 2015/05/12 12:50:46]

nit:
does it all fit in one line?
{} are not needed in any case

[mlamouri (slow - plz ping), 2015/05/19 21:56:17]

Chromium is using Android coding style in Java. What I wrote is allowed. Keeping
it in one line is allowed. Removing the braces isn't:
http://source.android.com/source/code-style.html

I prefer to keep it as-is given that it is allowed per coding style and having
it in one line is... unusual ;)

+                    nativeOnResume(mNativeMediaSession);
+                }
+                break;
+            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
+            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
+                nativeOnSuspend(mNativeMediaSession);
+                break;
+            case AudioManager.AUDIOFOCUS_LOSS:
+                abandonAudioFocus();
+                nativeOnSuspend(mNativeMediaSession);
+                break;
+        }
+    }
+
+    private native void nativeOnSuspend(long nativeMediaSession);
+    private native void nativeOnResume(long nativeMediaSession);
+}