Add field trial for balanced degradation preference.

webrtc/media/engine/webrtcvideoengine2.cc

Index: webrtc/media/engine/webrtcvideoengine2.cc
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index 03e97f776bfe7f42a063fd8a5b53410403915f50..5dfcb729b8ef869a79aed11a91cd322835b02da9 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -1751,6 +1751,8 @@ WebRtcVideoChannel2::WebRtcVideoSendStream::GetDegradationPreference() const {
       degradation_preference = DegradationPreference::kMaintainResolution;
     } else {
       degradation_preference = DegradationPreference::kMaintainFramerate;
+      if (webrtc::field_trial::IsEnabled("WebRTC-Video-BalancedDegradation"))

[mflodman1, 2017/06/13 09:23:19]

WDYT of, to avoid more nested if statements:

if (parameters_.options.is_screencast.value_or(false)) {
  degradation_preference = DegradationPreference::kMaintainResolution;
} else if (webrtc::field_trial::IsEnabled("WebRTC-Video-BalancedDegradation")) {
  degradation_preference = DegradationPreference::kBalanced;
} else {
  degradation_preference = DegradationPreference::kMaintainFramerate;
}

[åsapersson, 2017/06/13 10:17:15]

Done.

+        degradation_preference = DegradationPreference::kBalanced;
     }
   }
   return degradation_preference;