Is this for the internal Media Session code in Chromium or for the API?

Internal Media Session code. Mainly targeting for MediaSession on Desktop :)

Originally I was thinking of moving MediaSession::Type out, but I'm came up with the idea that we need another enum to tell MediaSession which type of player is joining, and the old MediaSession::Type is actually for audio focus (which only have two).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5d8eab739eb23c4fd27ba6a18b0e1afc15182321

commit 5d8eab739eb23c4fd27ba6a18b0e1afc15182321
Author: zqzhang <zqzhang@chromium.org>
Date: Fri Aug 26 20:34:30 2016

Split MediaContentType and AudioFocusType

The existing MediaSession::Type does not work well for
Pepper&WebRTC. Spliting MediaContentType for MediaPlayer and
AudioFocusType for MediaSession to gain more control of audio focus.

Explainer for this CL:
https://docs.google.com/a/google.com/document/d/1W4uRH8Wvgau0_GtMda4EOSXRtxFuFLhb9W77sJagJpI/edit?usp=sharing

BUG= 626351 

Review-Url: https://codereview.chromium.org/1996043002
Cr-Commit-Position: refs/heads/master@{#414800}

[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/android/browser_media_player_manager.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/android/media_web_contents_observer_android.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/android/media_web_contents_observer_android.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/media_web_contents_observer.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/media_web_contents_observer.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_browsertest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_controller.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_controller.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_controller_unittest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_controllers_manager.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_controllers_manager.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_delegate.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_delegate_android.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_delegate_android.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_delegate_android_browsertest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_delegate_default.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/media_session_delegate_default_browsertest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/media/session/pepper_playback_observer.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/browser/web_contents/web_contents_impl_unittest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/common/media/media_player_delegate_messages.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/renderer/media/android/webmediaplayer_android.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/renderer/media/renderer_webmediaplayer_delegate.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/renderer/media/renderer_webmediaplayer_delegate.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/renderer/media/renderer_webmediaplayer_delegate_browsertest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/renderer/media/webmediaplayer_ms.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/content/renderer/media/webmediaplayer_ms_unittest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/base/BUILD.gn
[add] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/base/media_content_type.cc
[add] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/base/media_content_type.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/blink/webmediaplayer_delegate.h
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/blink/webmediaplayer_impl.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/blink/webmediaplayer_impl_unittest.cc
[modify] https://crrev.com/5d8eab739eb23c4fd27ba6a18b0e1afc15182321/media/media.gyp