Get VideoCapturer stats via VideoTrackSourceInterface in StatsCollector,

webrtc/api/videocapturertracksource.cc

Index: webrtc/api/videocapturertracksource.cc
diff --git a/webrtc/api/videocapturertracksource.cc b/webrtc/api/videocapturertracksource.cc
index 1e9e35382c93e49b3d3f2da786b6048988d1f02f..66e372f5ac126927ab0437674f4c5e312ce1b6b5 100644
--- a/webrtc/api/videocapturertracksource.cc
+++ b/webrtc/api/videocapturertracksource.cc
@@ -360,6 +360,11 @@ void VideoCapturerTrackSource::Initialize(
   // Initialize hasn't succeeded until a successful state change has occurred.
 }
 
+bool VideoCapturerTrackSource::GetStats(Stats* stats) {
+  return video_capturer_->GetInputSize(&stats->input_width,
+                                       &stats->input_height);
+}
+
 void VideoCapturerTrackSource::Stop() {
   if (!started_) {
     return;