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..43b4d6aaa8e8a3993ec39267d6e65354ef503b74 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_stream_track_metrics_host_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 {
@@ -41,6 +43,15 @@ class RemoteMediaStreamTrackObserver
   DISALLOW_COPY_AND_ASSIGN(RemoteMediaStreamTrackObserver);
 };
 
+// We need an ID that is unique for this observer, within the current
+// renderer process, for the lifetime of the observer object. The
+// simplest approach is to just use the object's pointer value. We
+// store it in a uint64 which will be large enough regardless of
+// platform.
+uint64 MakeUniqueId(RemoteMediaStreamTrackObserver* observer) {
+  return reinterpret_cast<uint64>(reinterpret_cast<void*>(observer));
+}
+
 }  // namespace content
 
 namespace {
@@ -80,9 +91,21 @@ 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 MediaStreamTrackMetricsHost_AddTrack(
+      MakeUniqueId(this),
+      webkit_track_.source().type() == blink::WebMediaStreamSource::TypeAudio,
+      true));
 }
 
 RemoteMediaStreamTrackObserver::~RemoteMediaStreamTrackObserver() {
+  RenderThreadImpl::current()->Send(new MediaStreamTrackMetricsHost_RemoveTrack(
+      MakeUniqueId(this)));
+
   webrtc_track_->UnregisterObserver(this);
 }