Adding build switch for Opus that supports 120ms ptime.

webrtc/modules/audio_coding/audio_coding.gni

 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../../webrtc.gni")
 
 audio_codec_defines = []
 if (rtc_include_ilbc) {
   audio_codec_defines += [ "WEBRTC_CODEC_ILBC" ]
 }
 if (rtc_include_opus) {
   audio_codec_defines += [ "WEBRTC_CODEC_OPUS" ]
 }
+if (rtc_opus_support_120ms_ptime) {
+  audio_codec_defines += [ "WEBRTC_OPUS_SUPPORT_120MS_PTIME=1" ]
+} else {
+  audio_codec_defines += [ "WEBRTC_OPUS_SUPPORT_120MS_PTIME=0" ]
+}
 if (!build_with_mozilla) {
   if (current_cpu == "arm") {
     audio_codec_defines += [ "WEBRTC_CODEC_ISACFX" ]
   } else {
     audio_codec_defines += [ "WEBRTC_CODEC_ISAC" ]
   }
   audio_codec_defines += [ "WEBRTC_CODEC_G722" ]
 }
 if (!build_with_mozilla && !build_with_chromium) {
   audio_codec_defines += [ "WEBRTC_CODEC_RED" ]
 }
 
 audio_coding_defines = audio_codec_defines
 neteq_defines = audio_codec_defines