Adding build switch for Opus that supports 120ms ptime.

webrtc/webrtc.gni

Index: webrtc/webrtc.gni
diff --git a/webrtc/webrtc.gni b/webrtc/webrtc.gni
index 53dcae2b7c862d9b6b3d21b986fa2c763d8050c6..90b7d963ee2f6588e21d83298664a1bfde4eedfc 100644
--- a/webrtc/webrtc.gni
+++ b/webrtc/webrtc.gni
@@ -17,6 +17,10 @@ declare_args() {
   # Disable this to avoid building the Opus audio codec.
   rtc_include_opus = true
 
+  # Enable this if the Opus version upon which WebRTC is built support direct

[hlundin-webrtc, 2017/02/01 14:12:34]

supports

[minyue-webrtc, 2017/02/01 16:09:56]

will address it. 

Now I fix an error and PTAL again. and I will add Peter to review.

+  # encoding of 120 ms packets.
+  rtc_opus_support_120ms_ptime = false
+
   # Enable this to let the Opus audio codec change complexity on the fly.
   rtc_opus_variable_complexity = false