Wire up x-google-{min,start,max}-bitrate to WebRtcVoiceMediaChannel.

BUG=webrtc:6793

Review-Url: https://codereview.webrtc.org/2534173002
Cr-Original-Commit-Position: refs/heads/master@{#15337}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 13f1a0a9cab1aaa872b37d3a3aa3e894659c71c2
6 files changed