[MediaStream API] Adding MediaStreamTrack::getSourceInfos
This patch adds the functionality to list which webcams/micophones are available.

BUG=

Review URL: https://chromiumcodereview.appspot.com/15796004

git-svn-id: svn://svn.chromium.org/blink/trunk@151839 bbb929c8-8fbe-4397-9dbb-9b2b20218538
19 files changed