Implement support for creating MediaStreams based on existing tracks in a LocalMediaStream.
This adds supports for creating a new MediaStream based on tracks in another local media stream.
If a track originate from a remote source it is ignored.
BUG= See http://code.google.com/p/webrtc/issues/detail?id=389
TESTED= unit test + manual tests in a webpage.
Review URL: https://chromiumcodereview.appspot.com/
10910073
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@155990 0039d316-1c4b-4281-b951-d872f2087c98