Get VideoCapturer stats via VideoTrackSourceInterface in StatsCollector,

webrtc/api/mediastreaminterface.h

Index: webrtc/api/mediastreaminterface.h
diff --git a/webrtc/api/mediastreaminterface.h b/webrtc/api/mediastreaminterface.h
index 3e79b94f9efd7e7f143d09ddb50f269f8702e0e4..2fe76cc805617b8f1ef8bf9e22b5a122cebcad30 100644
--- a/webrtc/api/mediastreaminterface.h
+++ b/webrtc/api/mediastreaminterface.h
@@ -103,6 +103,11 @@ class VideoTrackSourceInterface
     : public MediaSourceInterface,
       public rtc::VideoSourceInterface<cricket::VideoFrame> {
  public:
+  struct Stats {
+    // Original frame size, before video adaptation.
+    int input_width;
+    int input_height;
+  };
   // Get access to the source implementation of cricket::VideoCapturer.
   // This can be used for receiving frames and state notifications.
   // But it should not be used for starting or stopping capturing.
@@ -127,6 +132,8 @@ class VideoTrackSourceInterface
   // the encoder.
   virtual bool needs_denoising() const = 0;
 
+  virtual bool GetStats(Stats* stats) = 0;
+
  protected:
   virtual ~VideoTrackSourceInterface() {}
 };