Add MediaStreamSource frame rate calculation to the tracker.

media/video/capture/video_capture_types.cc

Index: media/video/capture/video_capture_types.cc
diff --git a/media/video/capture/video_capture_types.cc b/media/video/capture/video_capture_types.cc
index ce5c354e290eed22fef06f69a067b4cf2d01265c..ce3f7b133b84d14adcd530a4f64fe2f297777543 100644
--- a/media/video/capture/video_capture_types.cc
+++ b/media/video/capture/video_capture_types.cc
@@ -11,13 +11,16 @@
 namespace media {
 
 VideoCaptureFormat::VideoCaptureFormat()
-    : frame_rate(0.0f), pixel_format(PIXEL_FORMAT_UNKNOWN) {}
+    : frame_rate(0.0f),
+      number_of_dropped_frames(0),
+      pixel_format(PIXEL_FORMAT_UNKNOWN) {}
 
 VideoCaptureFormat::VideoCaptureFormat(const gfx::Size& frame_size,
                                        float frame_rate,
                                        VideoPixelFormat pixel_format)
     : frame_size(frame_size),
       frame_rate(frame_rate),
+      number_of_dropped_frames(0),
       pixel_format(pixel_format) {}
 
 bool VideoCaptureFormat::IsValid() const {