[Android MR] Migrate MediaNotification for Cast/MediaFling

This CL migrates the MediaNotification into a separate CafNotificationController
class, to handle all the notification logic.

Bug: 711860
Change-Id: Ib01cd61f9e84a925a122a5f01161336d801caade
Reviewed-on: https://chromium-review.googlesource.com/1217752
Commit-Queue: Zhiqiang Zhang <zqzhang@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590461}
4 files changed