Implement Chrome glue code for MediaStreamTrack::Stop.
This cl is togehter with https://codereview.chromium.org/24070004/ what is needed to implement MediaStreamTrack::Stop and at the same time
keep the current behavior of MediaStream::Stop.

TEST= Open https://src.chromium.org/chrome/trunk/src/chrome/test/data/webrtc/manual/peerconnection-multi.html. Open the Java script console and type gLocalStream1.stop(). Notice that only video of the first video tag stop. This is as before. Refresh the page and type gLocalStream1.getVideoTracks()[].stop() and notice that both video tags stop playing video and the video camera is no longer in use.

BUG=293304

Review URL: https://codereview.chromium.org/26394004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229844 0039d316-1c4b-4281-b951-d872f2087c98
Move Extension policy handlers to live in chrome/browser/extensions.

This facilitates the refactoring of chrome/browser/policy into a layered
component.

BUG=271392

Review URL: https://codereview.chromium.org/26805008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229845 0039d316-1c4b-4281-b951-d872f2087c98
Fix a race on io_watcher_->success_response_ and io_watcher_->failed_response_
by making these counters into Atomic32 and using atomic operations to access them.

BUG=308590
R=rtenneti@chromium.org

Review URL: https://codereview.chromium.org/29063002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229846 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229845
SVN changes up to revision 229846