I think this bug very vaguely implies it's needed to make testing easier (except that it blocks the testing bug). Otherwise I'd not even file a bug for this but rather list this requirement in the test bug and submit the cl with the test bug in BUG=.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/52ec59e6f64784544c395fba8c448fea01033de4

commit 52ec59e6f64784544c395fba8c448fea01033de4
Author: zqzhang <zqzhang@chromium.org>
Date: Wed Mar 29 15:26:25 2017

Make media notification classes configurable

This CL makes the media notification classes configurable in the
following ways:

* Using Class<?> instead of class names for simplicity.
* Having a static map in MediaNotificationManager to look up the service
  class, receiver class, notification group name for a given
  notification ID.

BUG= 705925 

Review-Url: https://codereview.chromium.org/2776243003
Cr-Commit-Position: refs/heads/master@{#460394}

[modify] https://crrev.com/52ec59e6f64784544c395fba8c448fea01033de4/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaButtonReceiver.java
[modify] https://crrev.com/52ec59e6f64784544c395fba8c448fea01033de4/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java