MediaStream API: Update RTCDataChannel to match the specification
Just adding a bunch of attributes and deprecating one.

BUG=266333

Review URL: https://chromiumcodereview.appspot.com/21350002

git-svn-id: svn://svn.chromium.org/blink/trunk@155254 bbb929c8-8fbe-4397-9dbb-9b2b20218538