Adding build switch for Opus that supports 120ms ptime.

webrtc/modules/audio_coding/audio_coding.gni

Index: webrtc/modules/audio_coding/audio_coding.gni
diff --git a/webrtc/modules/audio_coding/audio_coding.gni b/webrtc/modules/audio_coding/audio_coding.gni
index 0f3a75fbac37859836d09aebff7b37647c1680cc..41dcf0044c898b7d1ca29490e3fa2cbd854e82d9 100644
--- a/webrtc/modules/audio_coding/audio_coding.gni
+++ b/webrtc/modules/audio_coding/audio_coding.gni
@@ -15,6 +15,11 @@ if (rtc_include_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" ]