Adding build switch for Opus that supports 120ms ptime.

webrtc/modules/audio_coding/acm2/acm_codec_database.cc

Index: webrtc/modules/audio_coding/acm2/acm_codec_database.cc
diff --git a/webrtc/modules/audio_coding/acm2/acm_codec_database.cc b/webrtc/modules/audio_coding/acm2/acm_codec_database.cc
index 4f5b263c24cbf71aabc1e61c45fbdf0016ec92f7..0fae75b91b4f8b7fff3ae28eec38eda0b690e51b 100644
--- a/webrtc/modules/audio_coding/acm2/acm_codec_database.cc
+++ b/webrtc/modules/audio_coding/acm2/acm_codec_database.cc
@@ -151,8 +151,12 @@ const ACMCodecDB::CodecSettings ACMCodecDB::codec_settings_[] = {
     // Opus supports frames shorter than 10ms,
     // but it doesn't help us to use them.
     // Mono and stereo.
+#if WEBRTC_OPUS_SUPPORT_120MS_PTIME
+    {5, {480, 960, 1920, 2880, 5760}, 0, 2},
+#else
     {4, {480, 960, 1920, 2880}, 0, 2},
 #endif
+#endif
     // Comfort noise for three different sampling frequencies.
     {1, {240}, 240, 1},
     {1, {480}, 480, 1},