GitLab

Added dataChannel.id text field to make it easier to test that Chrome/WebRTC reuses the dataChannel id on the same
peerConnection.

Feature added in issue:
https://code.google.com/p/webrtc/issues/detail?id=2646

BUG=NONE
TEST=Manual P2P call, dataChannel.id is only displayed when
dataChannel.readyState = 'open'.
NOTRY=TRUE

Review URL: https://codereview.chromium.org/405093004

Cr-Commit-Position: refs/heads/master@{#291887}