Implement getMediaDevices.
* Hook up two new function in the blink interface WebUserMediaClient in MediaStreamImpl through MediaStreamDispatcher to MediaStreamManager to enumerate audio and video input devices.
* Produces the same result as the current getSources API.
* The blink interface will be landed after this CL and browser test after that.
* Add audio output devices and group ID support is done in another CL.
BUG=338511
Review URL: https://codereview.chromium.org/
287383002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274608 0039d316-1c4b-4281-b951-d872f2087c98