Update RateStatistics to handle too-little-data case.

webrtc/video/receive_statistics_proxy.cc

Index: webrtc/video/receive_statistics_proxy.cc
diff --git a/webrtc/video/receive_statistics_proxy.cc b/webrtc/video/receive_statistics_proxy.cc
index 4757efa81b6cf3435212fea2f3e4dbb53d283734..8648fb62fbd7651366c515be0f3037a1ed007013 100644
--- a/webrtc/video/receive_statistics_proxy.cc
+++ b/webrtc/video/receive_statistics_proxy.cc
@@ -247,7 +247,7 @@ void ReceiveStatisticsProxy::OnDecodedFrame() {
 
   rtc::CritScope lock(&crit_);
   decode_fps_estimator_.Update(1, now);
-  stats_.decode_frame_rate = decode_fps_estimator_.Rate(now);
+  stats_.decode_frame_rate = decode_fps_estimator_.Rate(now).value_or(1);

[stefan-webrtc, 2016/06/02 07:16:42]

I'm not convinced this is correct. What if there are no samples? Shouldn't the
reported framerate be zero in that case?

[sprang_webrtc, 2016/06/02 08:09:32]

Yeah, you're right. I'll change it to default zero.
Same below.

[stefan-webrtc, 2016/06/02 08:14:39]

So, will we now ever be able to measure 1 fps? :)

[sprang, 2016/06/02 09:00:51]

Not if the actual rate is <= 1 fps. But slightly more and we'll round down to 1
:)
Do you think we should extend the window size for this, to say 2s? I'm
hesitant...

[stefan-webrtc, 2016/06/02 09:05:51]

Not sure. I'm mostly thinking whether it would make sense to report 1 fps if we
have 1 sample within the 1 second window in the frame rate case? Maybe it
doesn't? Seems like the way this is now implemented means that we will report 0
fps if the framerate is exactly 1 fps, which seems wrong?

[sprang_webrtc, 2016/06/02 12:23:50]

Done. PTAL

 }
 
 void ReceiveStatisticsProxy::OnRenderedFrame(int width, int height) {
@@ -257,7 +257,7 @@ void ReceiveStatisticsProxy::OnRenderedFrame(int width, int height) {
 
   rtc::CritScope lock(&crit_);
   renders_fps_estimator_.Update(1, now);
-  stats_.render_frame_rate = renders_fps_estimator_.Rate(now);
+  stats_.render_frame_rate = renders_fps_estimator_.Rate(now).value_or(1);
   render_width_counter_.Add(width);
   render_height_counter_.Add(height);
   render_fps_tracker_.AddSamples(1);