Cast: Refactor CastAudioSink and CastVideoSink

The code was not thread safe and did not support running only audio or
only video; which is now supported.

BUG=

Review URL: https://codereview.chromium.org/139743020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250249 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250249
Read compositor VSync information from platform, when possible

The current query of VSync information through the GL context can be unreliable
on platforms that can dynamically disable vblanks, or multi-monitor setups.
Preferentially query the VSync information through the platform windowing
system (presently: XRandR on CrOS) when possible.

BUG=328953
TEST=local build, run on CrOS snow

Review URL: https://codereview.chromium.org/138903025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250250 0039d316-1c4b-4281-b951-d872f2087c98
[Hotword] Add metric to checkbox to track enable/disable of hotwording.

BUG=325439, 289023

Review URL: https://codereview.chromium.org/153403004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250251 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250250
SVN changes up to revision 250251