GitLab

Add implementation to create OFFER message and handle ANSWER response.
Add the MirrorSettings which hold a set of default settings.

Bug: 734672
Change-Id: Ia6b9af5ac66e1f8f9496c0afaa335a22f40bb535
Reviewed-on: https://chromium-review.googlesource.com/1017235
Commit-Queue: Xiangjun Zhang <xjz@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555837}