GitLab

This CL adds the implementation to create an audio loopback stream
through Audio Service as requested.

Bug: 734672
Change-Id: Ifd78a1848c7979438401586c03f41758d996978e
Reviewed-on: https://chromium-review.googlesource.com/1141284
Commit-Queue: Xiangjun Zhang <xjz@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581017}