Turning on Opus 120ms frame length switch.

Chromium has adopted Opus 1.2.1 which allows 120ms frame encoding. It
is time to turn on the switch for building WebRTC with this feature.


Bug: webrtc:8042
TBR: kjellander@webrtc.org
Change-Id: I644b47cfb56f835695ef1263741cda6e3ee3d862
Reviewed-on: https://chromium-review.googlesource.com/586725
Commit-Queue: Minyue Li <minyue@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Felicia Lim <flim@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19173}
diff --git a/webrtc/webrtc.gni b/webrtc/webrtc.gni
index 676ab2f..e18464f 100644
--- a/webrtc/webrtc.gni
+++ b/webrtc/webrtc.gni
@@ -38,7 +38,7 @@
 
   # Enable this if the Opus version upon which WebRTC is built supports direct
   # encoding of 120 ms packets.
-  rtc_opus_support_120ms_ptime = false
+  rtc_opus_support_120ms_ptime = true
 
   # Enable this to let the Opus audio codec change complexity on the fly.
   rtc_opus_variable_complexity = false