Add mock AudioDeviceModule.

BUG=webrtc:4690

Review URL: https://codereview.webrtc.org/1844843003

Cr-Original-Commit-Position: refs/heads/master@{#12220}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: bc37fc8418da951cf56f5580731b8b034d1f12a6
5 files changed