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

content/browser/renderer_host/media/media_track_lifetime_metrics_host.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/renderer_host/media/media_track_lifetime_metrics_host.h"
+
+#include "base/metrics/histogram.h"
+#include "content/common/media/media_track_lifetime_metrics_messages.h"
+#include "content/public/browser/render_process_host.h"
+
+// We use a histogram with a maximum bucket of 16 hours to infinity
+// for track durations.
+#define UMA_HISTOGRAM_TIMES_16H(name, sample)                        \
+  UMA_HISTOGRAM_CUSTOM_TIMES(name, sample,                           \
+                             base::TimeDelta::FromMilliseconds(100), \
+                             base::TimeDelta::FromHours(16),         \
+                             50);
+
+namespace content {
+
+MediaTrackLifetimeMetricsHost::MediaTrackLifetimeMetricsHost(
+    RenderProcessHost* owner)
+    : BrowserMessageFilter(MediaTrackLifetimeMetricsHostMsgStart),
+      owner_(owner) {
+  owner_->AddObserver(this);
+}
+
+MediaTrackLifetimeMetricsHost::~MediaTrackLifetimeMetricsHost() {
+  owner_->RemoveObserver(this);
+
+  DCHECK(tracks_.empty());
+}
+
+bool MediaTrackLifetimeMetricsHost::OnMessageReceived(
+    const IPC::Message& message,
+    bool* message_was_ok) {
+  bool handled = true;
+
+  IPC_BEGIN_MESSAGE_MAP_EX(MediaTrackLifetimeMetricsHost,
+                           message,
+                           *message_was_ok)
+    IPC_MESSAGE_HANDLER(MediaTrackLifetimeMetrics_AddTrack, OnAddTrack)
+    IPC_MESSAGE_HANDLER(MediaTrackLifetimeMetrics_RemoveTrack, OnRemoveTrack)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP_EX()
+
+  return handled;
+}
+
+void MediaTrackLifetimeMetricsHost::RenderProcessExited(
+    RenderProcessHost* host,
+    base::ProcessHandle handle,
+    base::TerminationStatus status,
+    int exit_code) {
+  DCHECK_EQ(owner_, host);
+
+  // Our render process has exited. We won't receive any more IPC
+  // messages from it. Assume all tracks ended now.
+  for (TrackMap::iterator it = tracks_.begin();
+       it != tracks_.end();
+       ++it) {
+    ReportDuration(it->second.first, it->second.second);

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

nit: can you use temp variables instead of second.first second.second. My memory
fails to tell me what they mean.

[Jói, 2014/03/11 17:36:33]

I added a temp IsAudioPlusTimestamp variable then I do audio_and_timestamp.first
and audio_and_timestamp.second, that should be pretty clear.

+  }
+  tracks_.clear();
+}
+
+void MediaTrackLifetimeMetricsHost::OnAddTrack(const std::string& id,
+                                               bool is_audio) {
+  DCHECK(tracks_.find(id) == tracks_.end());

[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. So
the unique identifier is ms id + track id.

+
+  tracks_[id] = IsAudioPlusTimestamp(is_audio, base::TimeTicks::Now());
+}
+
+void MediaTrackLifetimeMetricsHost::OnRemoveTrack(const std::string& id) {
+  DCHECK(tracks_.find(id) != tracks_.end());
+
+  IsAudioPlusTimestamp& info = tracks_[id];
+  ReportDuration(info.first, info.second);
+  tracks_.erase(id);
+}
+
+void MediaTrackLifetimeMetricsHost::ReportDuration(bool is_audio,
+                                                   base::TimeTicks start_time) {
+  base::TimeDelta duration = start_time - base::TimeTicks::Now();
+  if (is_audio) {
+    UMA_HISTOGRAM_TIMES_16H("WebRTC.ReceivedAudioTrackDuration", duration);

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

Will we not have the same problem for local tracks and need to track the
duration in the same way? 
ie- extend the identifier to be more than just bool audio?

I guess we can also argue what it is we want to track. Is it the source duration
or the track duration? 
I mean- you are supposed to be able to clone all sort of tracks, both local and
remote and I guess you only want to track the duration of the original track or
source. But starting talking about sources here might also be confusing... Are
we only going to track the original - none cloned track? How about adding a
comment about that somewhere and continue to have the UMA histogram called
TrackDuration?

[Jói, 2014/03/11 17:36:33]

I think we had settled on track duration in the design phase, but I agree with
your concerns and I think it would be better to not count locally-cloned tracks.
For now I suggest just documenting how this currently works, which I would do in
histograms.xml.

Do cloned tracks actually get reflected as RemoteMediaStreamTrackObserver
interfaces in RemoteMediaStreamImpl?

For sent tracks, I will expand this class when appropriate as I add that
tracking. The distinction is not needed for now.

+  } else {
+    UMA_HISTOGRAM_TIMES_16H("WebRTC.ReceivedVideoTrackDuration", duration);
+  }
+}
+
+}  // namespace content