No longer need to expose them in content/public as we now notify the initial information when adding observers.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fa29809ee94916e79cd5e25060cd03ed3b1bb46f

commit fa29809ee94916e79cd5e25060cd03ed3b1bb46f
Author: zqzhang <zqzhang@chromium.org>
Date: Wed Mar 22 17:24:33 2017

Clean up MediaSessionImpl state interfaces

This CL cleans up the MediaSessionImpl state interfaces,
especially "suspended" and "paused".

BUG= 702627 

Review-Url: https://codereview.chromium.org/2758773003
Cr-Commit-Position: refs/heads/master@{#458791}

[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/audio_focus_delegate_android.cc
[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/audio_focus_manager_unittest.cc
[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/media_session_controller.cc
[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/media_session_controller_unittest.cc
[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/media_session_impl.cc
[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/media_session_impl.h
[modify] https://crrev.com/fa29809ee94916e79cd5e25060cd03ed3b1bb46f/content/browser/media/session/media_session_impl_browsertest.cc