Add FullStack test for simulcast screenshare mode.

webrtc/video/video_quality_test.h

Index: webrtc/video/video_quality_test.h
diff --git a/webrtc/video/video_quality_test.h b/webrtc/video/video_quality_test.h
index 564d49936bf80e82988f5d9bdbc07762c11717fa..2631d35da0c56bae040843f0ae90b060e8922a4a 100644
--- a/webrtc/video/video_quality_test.h
+++ b/webrtc/video/video_quality_test.h
@@ -14,6 +14,7 @@
 #include <string>
 #include <vector>
 
+#include "webrtc/modules/video_coding/codecs/vp8/simulcast_encoder_adapter.h"
 #include "webrtc/test/call_test.h"
 #include "webrtc/test/frame_generator.h"
 #include "webrtc/test/testsupport/trace_to_stderr.h"
@@ -129,6 +130,8 @@ class VideoQualityTest : public test::CallTest {
   std::unique_ptr<test::TraceToStderr> trace_to_stderr_;
   std::unique_ptr<test::FrameGenerator> frame_generator_;
   std::unique_ptr<VideoEncoder> video_encoder_;
+  std::unique_ptr<VideoEncoderFactory> vp8_encoder_factory_;
+
   std::vector<std::unique_ptr<VideoEncoder>> thumbnail_encoders_;
   std::vector<VideoSendStream::Config> thumbnail_send_configs_;
   std::vector<VideoEncoderConfig> thumbnail_encoder_configs_;