zhihuang 1c378ed83b Relanding: Adding support for Unified Plan offer/answer negotiation to the mediasession layer.
This layer takes in a simplified "options" struct and the current local description,
and generates a new offer/answer. Previously the options struct assumed there would
only be one media description per media type (audio/video), but it now supports
N number of audio/video descriptions.

The |add_legacy_stream| options is removed from the mediasession.cc/.h
in this CL.

The next step is to add the ability for PeerConnection/WebRtcSession to create
"options" to represent multiple RtpTransceivers, and apply the Unified Plan
descriptions correctly. Right now, only Plan B descriptions will be
generated in unit tests.

BUG=chromium:465349

Review-Url: https://codereview.webrtc.org/2991693002
Cr-Original-Commit-Position: refs/heads/master@{#19343}
Committed: a77e6bbd30
Review-Url: https://codereview.webrtc.org/2991693002
Cr-Commit-Position: refs/heads/master@{#19394}
2017-08-17 21:10:50 +00:00
..
2016-04-26 12:28:18 +00:00