Makes WebContentsVideoCaptureDevice inherit from VideoCaptureDevice and removes unnecessary code.
The lock in ThreadSafeCaptureOracle is still used to protect client_ because it can be accessed from both the browser UI thread and RenderVideoFrame worker thread.

BUG=297848

Review URL: https://codereview.chromium.org/24900002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226047 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226047
Make the local discovery UI update itself based on whether the user is logged in

Update chrome://devices/ as the user's login state changes, refresh the printer
list, and add/remove login promos.

BUG=299963

Review URL: https://codereview.chromium.org/24996006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226048 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226048