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 0543dff3f383f628f102535b1c3e84d90ca930ee..cb539614be72af2587954103d79150e92209eb29 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;