Adding build switch for Opus that supports 120ms ptime.

BUG=webrtc:7097

TEST=Set "ptime=120", try WebRTC calls over custom build Chromium with and without Opus 120ms. Try both Chromium w <-> Chromium w and Chromium w <-> Chromium w/o

Review-Url: https://codereview.webrtc.org/2668633004
Cr-Original-Commit-Position: refs/heads/master@{#16408}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 2e03c6611927af6ed08cf967b95342744ff329b6
7 files changed