Add stats for used video codec type for a sent video stream:

webrtc/video/send_statistics_proxy.cc

Index: webrtc/video/send_statistics_proxy.cc
diff --git a/webrtc/video/send_statistics_proxy.cc b/webrtc/video/send_statistics_proxy.cc
index 32b79023c8495de9a06150197b80b135e1628239..b87b96ee936bdb268f025aff83f4f7269df3511a 100644
--- a/webrtc/video/send_statistics_proxy.cc
+++ b/webrtc/video/send_statistics_proxy.cc
@@ -20,6 +20,35 @@
 #include "webrtc/system_wrappers/interface/metrics.h"
 
 namespace webrtc {
+namespace {
+// Used by histograms. Values of entries should not be changed.
+enum HistogramCodecType {
+  kVideoVp8 = 0,

[pbos-webrtc, 2015/10/26 13:19:03]

I'd prefer unknown to be zero, and then set explicit values for VP9 and H264 as
well, so that we don't risk that they change.

[åsapersson, 2015/10/26 14:19:53]

Done.

+  kVideoVp9,
+  kVideoH264,
+  kVideoUnknown = 19,
+  kVideoMax = 20,

[pbos-webrtc, 2015/10/26 13:19:03]

I think you can pick something larger if this isn't supposed to change, like 64.
It shouldn't matter either way.

[åsapersson, 2015/10/26 14:19:53]

Done.

+};
+
+HistogramCodecType PayloadNameToHistogramCodecType(
+    const std::string& payload_name) {
+  if (payload_name == "VP8") {
+    return kVideoVp8;
+  } else if (payload_name == "VP9") {
+    return kVideoVp9;
+  } else if (payload_name == "H264") {
+    return kVideoH264;
+  } else {
+    return kVideoUnknown;
+  }
+}
+
+void UpdateCodecTypeHistogram(const std::string& payload_name) {
+  RTC_HISTOGRAM_ENUMERATION("WebRTC.Video.Encoder.CodecType",
+      PayloadNameToHistogramCodecType(payload_name), kVideoMax);
+}
+}  // namespace
+
 
 const int SendStatisticsProxy::kStatsTimeoutMs = 5000;
 
@@ -32,6 +61,7 @@ SendStatisticsProxy::SendStatisticsProxy(Clock* clock,
       last_sent_frame_timestamp_(0),
       max_sent_width_per_timestamp_(0),
       max_sent_height_per_timestamp_(0) {
+  UpdateCodecTypeHistogram(config_.encoder_settings.payload_name);
 }
 
 SendStatisticsProxy::~SendStatisticsProxy() {