New flag is_screencast in VideoOptions.

webrtc/media/base/mediachannel.h

Index: webrtc/media/base/mediachannel.h
diff --git a/webrtc/media/base/mediachannel.h b/webrtc/media/base/mediachannel.h
index 8f15878ecd80efcff2fe1c4a438bf8f30a52003e..3830abf916c938eab80231285b443361897218fc 100644
--- a/webrtc/media/base/mediachannel.h
+++ b/webrtc/media/base/mediachannel.h
@@ -254,12 +254,14 @@ struct VideoOptions {
     SetFrom(&video_noise_reduction, change.video_noise_reduction);
     SetFrom(&suspend_below_min_bitrate, change.suspend_below_min_bitrate);
     SetFrom(&screencast_min_bitrate_kbps, change.screencast_min_bitrate_kbps);
+    SetFrom(&is_screencast, change.is_screencast);
   }
 
   bool operator==(const VideoOptions& o) const {
     return video_noise_reduction == o.video_noise_reduction &&
            suspend_below_min_bitrate == o.suspend_below_min_bitrate &&
-           screencast_min_bitrate_kbps == o.screencast_min_bitrate_kbps;
+           screencast_min_bitrate_kbps == o.screencast_min_bitrate_kbps &&
+           is_screencast == o.is_screencast;
   }
 
   std::string ToString() const {
@@ -270,6 +272,7 @@ struct VideoOptions {
                          suspend_below_min_bitrate);
     ost << ToStringIfSet("screencast min bitrate kbps",
                          screencast_min_bitrate_kbps);
+    ost << ToStringIfSet("is_screencast ", is_screencast);
     ost << "}";
     return ost.str();
   }
@@ -288,6 +291,11 @@ struct VideoOptions {
   // the PeerConnection constraint 'googScreencastMinBitrate'. It is
   // copied to the encoder config by WebRtcVideoChannel2.
   rtc::Optional<int> screencast_min_bitrate_kbps;
+  // Set by screencast sources. Implies selection of encoding settings
+  // suitable for screencast. Most likely not the right way to do
+  // things, e.g., screencast of a text document and screencast of a
+  // youtube video have different needs.
+  rtc::Optional<bool> is_screencast;
 
  private:
   template <typename T>