Add histogram stats for average QP per frame for VP8 (for sent video streams):

webrtc/video/send_statistics_proxy_unittest.cc

Index: webrtc/video/send_statistics_proxy_unittest.cc
diff --git a/webrtc/video/send_statistics_proxy_unittest.cc b/webrtc/video/send_statistics_proxy_unittest.cc
index a98505f84d1e01f3837a05d588826377853096b6..5c04b4bb6c2ba9dec905125fe173b7687c03b14f 100644
--- a/webrtc/video/send_statistics_proxy_unittest.cc
+++ b/webrtc/video/send_statistics_proxy_unittest.cc
@@ -327,6 +327,29 @@ TEST_F(SendStatisticsProxyTest, SwitchContentTypeUpdatesHistograms) {
   EXPECT_EQ(1, test::NumHistogramSamples("WebRTC.Video.InputWidthInPixels"));
 }
 
+TEST_F(SendStatisticsProxyTest, VerifyQpHistogramStats) {
+  test::ClearHistograms();
+  const int kMinRequiredSamples = 200;
+  const int kQpIdx0 = 21;
+  const int kQpIdx1 = 39;
+  EncodedImage encoded_image;
+
+  RTPVideoHeader rtp_video_header;
+  rtp_video_header.codec = kRtpVideoVp8;
+
+  for (int i = 0; i < kMinRequiredSamples; ++i) {
+    rtp_video_header.simulcastIdx = 0;
+    encoded_image.qp_ = kQpIdx0;
+    statistics_proxy_->OnSendEncodedImage(encoded_image, &rtp_video_header);
+    rtp_video_header.simulcastIdx = 1;
+    encoded_image.qp_ = kQpIdx1;
+    statistics_proxy_->OnSendEncodedImage(encoded_image, &rtp_video_header);
+  }
+  statistics_proxy_.reset();
+  EXPECT_EQ(2, test::NumHistogramSamples("WebRTC.Video.Encoded.Qp.Vp8"));
+  EXPECT_EQ(kQpIdx1, test::LastHistogramSample("WebRTC.Video.Encoded.Qp.Vp8"));

[stefan-webrtc, 2016/03/22 15:12:46]

Shouldn't this be the average of 21 and 39?

[åsapersson, 2016/03/22 15:29:46]

QP is stored per ssrc e.g.
two qp samples should be recorded (one for each stream): 
simulcast_idx: 0 -> ssrcs[0] average of 21.
simulcast_idx: 1 -> ssrcs[1] average of 39.

+}
+
 TEST_F(SendStatisticsProxyTest, NoSubstreams) {
   uint32_t excluded_ssrc =
       std::max(