Add histogram stats for average QP per frame for VP9 (for sent video streams):

webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc

Index: webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
diff --git a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
index 1ca08c1ec8dcbefa7afeb435cd6c44952dfc6f07..0e7c35d73dd6c4b05c1d51544de30a52341763ca 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -694,6 +694,9 @@ int VP9EncoderImpl::GetEncodedLayerFrame(const vpx_codec_cx_pkt* pkt) {
     encoded_image_.capture_time_ms_ = input_image_->render_time_ms();
     encoded_image_._encodedHeight = raw_->d_h;
     encoded_image_._encodedWidth = raw_->d_w;
+    int qp = -1;
+    vpx_codec_control(encoder_, VP8E_GET_LAST_QUANTIZER, &qp);

[mflodman, 2016/04/11 07:00:23]

I assume VP8 is the correct parameter here, but just checking.

[åsapersson, 2016/04/11 07:28:15]

Think so, it says that it is supported for VP9.

+    encoded_image_.qp_ = qp;
     encoded_complete_callback_->Encoded(encoded_image_, &codec_specific,
                                         &frag_info);
   }