[Android] A prototype of the interactive media notification.
MediaSession notifies WebContentsDelegate when to show/hide the controls.
ChromeTab's delegate implementation uses NotificationMediaPlaybackControls for the
notification. Notification is implemented similar to the Cast one.
WebContentsDelegate gets the necessary information from MediaSession via
MediaControlsDelegate interface provided by WebContents.
BUG=470600
TEST=Manual
Review URL: https://codereview.chromium.org/
1159113006
Cr-Commit-Position: refs/heads/master@{#337844}