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..295b740216e8e4e5928d454be27f6b09b7395e12 100644
--- a/content/renderer/media/remote_media_stream_impl.cc
+++ b/content/renderer/media/remote_media_stream_impl.cc
@@ -8,8 +8,10 @@
 
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
+#include "content/common/media/media_track_lifetime_metrics_messages.h"
 #include "content/renderer/media/media_stream.h"
 #include "content/renderer/media/media_stream_dependency_factory.h"
+#include "content/renderer/render_thread_impl.h"
 #include "third_party/WebKit/public/platform/WebString.h"
 
 namespace content {
@@ -80,9 +82,20 @@ RemoteMediaStreamTrackObserver::RemoteMediaStreamTrackObserver(
       webrtc_track_(webrtc_track),
       webkit_track_(webkit_track) {
   webrtc_track->RegisterObserver(this);
+
+  // We need to mirror the lifetime state for tracks to the browser
+  // process so that the duration of tracks can be accurately
+  // reported, because of RenderProcessHost::FastShutdownIfPossible,
+  // which in many cases will simply kill the renderer process.
+  RenderThreadImpl::current()->Send(new MediaTrackLifetimeMetrics_AddTrack(

[perkj_chrome, 2014/03/11 08:05:21]

Can we do this in a virtual method instead so I can write a unit test for the
track observer that can't deal whith the static render thread and ipc messages?
I am refactoring this class currently to support having the remote video tracks
be a source to the chrome tracks as discussed.

I can do that in my cl if you think that is the correct approach.

[Jói, 2014/03/11 17:36:33]

Sure, sounds good.

+      webkit_track_.id().utf8(),

[perkj_chrome, 2014/03/11 08:05:21]

To make this a bit harder - the same track can theoretically be received in
multiple mediastreams on the same PeerConnection. They will have the same id.

[Jói, 2014/03/11 17:36:33]

I'm now using the MediaStream ID plus the track ID.

+      webkit_track_.source().type() == blink::WebMediaStreamSource::TypeAudio));
 }
 
 RemoteMediaStreamTrackObserver::~RemoteMediaStreamTrackObserver() {
+  RenderThreadImpl::current()->Send(new MediaTrackLifetimeMetrics_RemoveTrack(

[perkj_chrome, 2014/03/11 08:05:21]

dito

[Jói, 2014/03/11 17:36:33]

Done.

+      webkit_track_.id().utf8()));
+
   webrtc_track_->UnregisterObserver(this);
 }