Adding audio only mode to video loopback test.

webrtc/video/video_loopback.cc

Index: webrtc/video/video_loopback.cc
diff --git a/webrtc/video/video_loopback.cc b/webrtc/video/video_loopback.cc
index b64b314d10205975417f6a3f464eb731a1b85319..91a0423931885324b681267263d5306c96075c56 100644
--- a/webrtc/video/video_loopback.cc
+++ b/webrtc/video/video_loopback.cc
@@ -196,6 +196,8 @@ DEFINE_bool(audio, false, "Add audio stream");
 DEFINE_bool(audio_video_sync, false, "Sync audio and video stream (no effect if"
     " audio is false)");
 
+DEFINE_bool(mute_video, false, "Mute video stream");

[stefan-webrtc, 2016/09/07 13:12:10]

Can we call this "video" instead to align it with "audio"?

[minyue-webrtc, 2016/09/08 15:38:24]

Done.

+
 DEFINE_string(
     force_fieldtrials,
     "",
@@ -231,7 +233,7 @@ void Loopback() {
 
   VideoQualityTest::Params params;
   params.common = {flags::FLAGS_send_side_bwe, call_bitrate_config};
-  params.video = {true,
+  params.video = {!flags::FLAGS_mute_video,
                   flags::Width(),
                   flags::Height(),
                   flags::Fps(),