Add metrics to track the duration of tracks received over a PeerConnection.

content/renderer/media/remote_media_stream_impl.cc

Index: content/renderer/media/remote_media_stream_impl.cc
diff --git a/content/renderer/media/remote_media_stream_impl.cc b/content/renderer/media/remote_media_stream_impl.cc
index 66bdb60821d460328d74c65a2bb76744a013e93a..4e85e60c7325b35110ff1c15c2e35c0cd1083711 100644
--- a/content/renderer/media/remote_media_stream_impl.cc
+++ b/content/renderer/media/remote_media_stream_impl.cc
@@ -7,7 +7,9 @@
 #include <string>
 
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/time/time.h"
 #include "content/renderer/media/media_stream.h"
 #include "content/renderer/media/media_stream_dependency_factory.h"
 #include "third_party/WebKit/public/platform/WebString.h"
@@ -38,6 +40,10 @@ class RemoteMediaStreamTrackObserver
   scoped_refptr<webrtc::MediaStreamTrackInterface> webrtc_track_;
   blink::WebMediaStreamTrack webkit_track_;
 
+  // Used to calculate duration of the track for a metric logged at
+  // destruction time.
+  base::TimeTicks creation_time_;
+
   DISALLOW_COPY_AND_ASSIGN(RemoteMediaStreamTrackObserver);
 };
 
@@ -78,11 +84,28 @@ RemoteMediaStreamTrackObserver::RemoteMediaStreamTrackObserver(
     const blink::WebMediaStreamTrack& webkit_track)
     : state_(webrtc_track->state()),
       webrtc_track_(webrtc_track),
-      webkit_track_(webkit_track) {
+      webkit_track_(webkit_track),
+      creation_time_(base::TimeTicks::Now()) {
   webrtc_track->RegisterObserver(this);
 }
 
 RemoteMediaStreamTrackObserver::~RemoteMediaStreamTrackObserver() {

[perkj_chrome, 2014/03/05 09:39:17]

If you close a tab - which I guess is very common when you quit a call- the
render process destructors don't run. Is that a problem for your history?

+  // Emit the duration of the track to a histogram (one for audio, one
+  // for video).
+  base::TimeDelta duration = base::TimeTicks::Now() - creation_time_;
+  std::string histogram_name = "WebRTC.ReceivedVideoTrackDuration";
+  if (webkit_track_.source().type() == blink::WebMediaStreamSource::TypeAudio) {
+    histogram_name = "WebRTC.ReceivedAudioTrackDuration";
+  } else {
+    DCHECK(webkit_track_.source().type() ==
+           blink::WebMediaStreamSource::TypeVideo);
+  }
+  UMA_HISTOGRAM_CUSTOM_TIMES(histogram_name,

[Ami GONE FROM CHROMIUM, 2014/03/05 08:44:27]

This is a bug - the name parameter to UMA macros must be a compile-time
constant.

[Alexei Svitkine (slow), 2014/03/05 14:23:37]

The histogram macros cache the Histogram object after the first invocation at
the call site, so while the name doesn't have to be a string literal (like it
does for actions), you do need a separate macro callsite for each distinct
histogram name you're logging.

+                             duration,
+                             base::TimeDelta::FromMilliseconds(100),
+                             base::TimeDelta::FromHours(16),
+                             50);
+
   webrtc_track_->UnregisterObserver(this);
 }