Link MediaSessionTabHelper with native MediaSession [CL is going to be split]

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

 // Copyright 2014 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_public.browser;
 
 import android.graphics.Bitmap;
 import android.graphics.Rect;
 import android.os.Parcelable;
 
@@ skipping 288 matching lines @@
     int getThemeColor();
 
     /**
      * Requests a snapshop of accessibility tree. The result is provided asynchronously
      * using the callback
      * @param callback The callback to be called when the snapshot is ready. The callback
      *                 cannot be null.
      */
     void requestAccessibilitySnapshot(AccessibilitySnapshotCallback callback);
 
-    /**
-     * Resumes the current media session.
-     */
-    void resumeMediaSession();
-
-    /**
-     * Suspends the current media session.
-     */
-    void suspendMediaSession();
-
-    /**
-     * Stops the current media session.
-     */
-    void stopMediaSession();
+    void addMediaSessionDelegate(MediaSessionDelegate delegate);

[boliu, 2016/10/19 20:39:40]

nit: s/add/set/ ?

[Zhiqiang Zhang (Slow), 2016/10/20 16:22:32]

Not really, we allow adding multiple MediaSessionDelegates.

[boliu, 2016/10/20 16:28:33]

Usually you can have only one "delegate", but multiple "observers". Are these
supposed to be observers?

[Zhiqiang Zhang (Slow), 2016/10/20 17:07:03]

Actually "delegate" inherits from "observer", a delegate can both observe
MediaSession changes and perform actions on MediaSession. Ideally this could be
solved by adding a Java counterpart of MediaSession, but we don't have plans.

We haven't come up with a better name yet. Do you have any suggestion? Or Anton
has some ideas?

[boliu, 2016/10/20 17:10:19]

Feels like that fact should live in the embedder not content.

Like WebContents has a Delegate and a bunch of Observers. It doesn't care if the
embedder's Delegate also implements the Observer. (Although embedder have to be
careful of ownership.(

On the other hand, does this really need to be that complicated? I'd suggest
trying to simplify if possible, without actually knowing any of this code

 
     /**
      * Add an observer to the WebContents
      *
      * @param observer The observer to add.
      */
     void addObserver(WebContentsObserver observer);
 
     /**
      * Remove an observer from the WebContents
@@ skipping 28 matching lines @@
      *                 0 means unlimited.
      * @param bypassCache If true, {@link url} is requested from the server even if it is present in
      *                 the browser cache.
      * @param callback The callback which will be called when the bitmaps are received from the
      *                 renderer.
      * @return The unique id of the download request
      */
     public int downloadImage(String url, boolean isFavicon, int maxBitmapSize,
             boolean bypassCache, ImageDownloadCallback callback);
 }