The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8fae3446b59330bb28aba760c7dbde3d7e80a6f7

commit 8fae3446b59330bb28aba760c7dbde3d7e80a6f7
Author: zqzhang <zqzhang@chromium.org>
Date: Sun Dec 18 18:40:56 2016

[MediaSession] Add playbackState attribute to Blink MediaSession and use it to determine playback state

This CL implements MediaSession.playbackState attribute, and
propagates the attribute through mojo to MediaSessionImpl. The
attribute is then used to determine the actual playback state.

Basically, the behavior change is: when the page media is
currently paused while playbackState is "playing", we show
a "pause" button instead of "playing" button.

Spec PR:
https://github.com/WICG/mediasession/pull/152

BUG= 674470 

Review-Url: https://codereview.chromium.org/2583463002
Cr-Commit-Position: refs/heads/master@{#439375}

[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/media_session_impl.cc
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/media_session_impl.h
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/media_session_impl_browsertest.cc
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/media_session_service_impl.cc
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/media_session_service_impl.h
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/mock_media_session_player_observer.cc
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/content/browser/media/session/mock_media_session_player_observer.h
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/property-access-on-cached-properties-after-frame-navigated-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/property-access-on-cached-properties-after-frame-removed-and-gced-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/property-access-on-cached-properties-after-frame-removed-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/property-access-on-cached-window-after-frame-navigated-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/property-access-on-cached-window-after-frame-removed-and-gced-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/property-access-on-cached-window-after-frame-removed-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/fast/dom/Window/resources/window-property-collector.js
[add] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/media/mediasession/mediasession-playbackstate-expected.txt
[add] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/media/mediasession/mediasession-playbackstate.html
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/media/mediasession/mojo/media-control-action-reaches-client.html
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/media/mediasession/mojo/media-control-set-handler-notifies-service.html
[add] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/media/mediasession/mojo/playback-state-propagated.html
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/media/mediasession/mojo/resources/mediasessionservice-mock.js
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/Source/modules/mediasession/MediaSession.cpp
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/Source/modules/mediasession/MediaSession.h
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/Source/modules/mediasession/MediaSession.idl
[modify] https://crrev.com/8fae3446b59330bb28aba760c7dbde3d7e80a6f7/third_party/WebKit/public/platform/modules/mediasession/media_session.mojom

I think this is fixed :)