Strip out stream counting from AudioRendererHost.

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 4a3b2c7ce211d146e0517b63d327e78a2d0cbd5e..286e15c15299b48c04d8dc42ead347c6d6d68654 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -319,6 +319,11 @@ bool has_done_stun_trials = false;
 
 #endif
 
+// Tracks the maximum number of simultaneous output streams browser-wide.
+// Accessed on UI thread.
+base::LazyInstance<media::AudioStreamsTracker> g_audio_streams_tracker =
+    LAZY_INSTANCE_INITIALIZER;
+
 // the global list of all renderer processes
 base::LazyInstance<IDMap<RenderProcessHost*>>::Leaky g_all_hosts =
     LAZY_INSTANCE_INITIALIZER;
@@ -782,6 +787,19 @@ RenderProcessHostImpl::~RenderProcessHostImpl() {
     BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
                             base::Bind(&RemoveShaderInfo, GetID()));
   }
+
+  // If we had any streams, report UMA stats for the maximum number of
+  // simultaneous streams for this render process and for the whole browser
+  // process since last reported.
+  if (audio_streams_tracker_.max_stream_count() > 0) {
+    UMA_HISTOGRAM_CUSTOM_COUNTS("Media.AudioRendererIpcStreams",
+                                audio_streams_tracker_.max_stream_count(), 1,
+                                50, 51);
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "Media.AudioRendererIpcStreamsTotal",
+        g_audio_streams_tracker.Get().max_stream_count(), 1, 100, 101);

[ncarter (slow), 2017/01/31 18:33:12]

This logging used to happen each time a MessageFilter was destroyed; now it
happens each time a RenderProcessHostImpl is destroyed. This is not the same:
each type of MessageFilter can be created and destroyed multiple times for a
particular RenderProcessHostImpl -- in particular, this happens in the crash /
sad tab case -- the RenderProcessHostImpl stays around, but
CreateMessageFilters() occurs again, creating a second generation of message
filters for the RPH instance, if the tab is reloaded.

So this isn't the same as the old behavior. Are you sure it's what you intend?
In particular I worry that if you force-kill a process that has active audio
streams, will the count actually fall to zero, or will you wind up in an
incorrect state?

It would be good to have browsertests for that case. histogram_tester.h in base
can be useful for that sort of test.

[DaleCurtis, 2017/01/31 22:08:31]

Ah, I didn't know multiple sets of MessageFilter's can be created like this. The
spirit of the logging was render process shutdown, though the implementation was
not. I'd actually like to just delete these metrics; I don't think they're all
that useful. +grunell for commentary.

[Henrik Grunell, 2017/02/03 08:52:20]

Sorry Dale, I missed that I was supposed to reply to this. I think we can remove
these metrics. It was added for the mixing experiment which is deprecated in its
current form. I don't see any reason to keep it around. If we'll work on
changing the mixing later on, we can re-add these or other metrics.

Olga and Max: are they useful in the separate process work? (I doubt that.)

[DaleCurtis, 2017/02/06 22:19:02]

Deleted, thanks!

+    g_audio_streams_tracker.Get().ResetMaxStreamCount();
+  }
 }
 
 bool RenderProcessHostImpl::Init() {
@@ -1555,7 +1573,15 @@ int RenderProcessHostImpl::VisibleWidgetCount() const {
   return visible_widgets_;
 }
 
-void RenderProcessHostImpl::AudioStateChanged() {
+void RenderProcessHostImpl::OnAudioStreamAdded() {
+  audio_streams_tracker_.IncreaseStreamCount();
+  g_audio_streams_tracker.Get().IncreaseStreamCount();
+  UpdateProcessPriority();

[Max Morin, 2017/01/30 11:47:07]

It probably makes sense to only UpdateProcessPriority if the value of
audio_streams_tracker_.has_streams() changed.

[DaleCurtis, 2017/02/06 22:19:02]

UpdateProcessPriority() takes care of this.

+}
+
+void RenderProcessHostImpl::OnAudioStreamRemoved() {
+  audio_streams_tracker_.DecreaseStreamCount();
+  g_audio_streams_tracker.Get().DecreaseStreamCount();
   UpdateProcessPriority();
 }
 
@@ -2815,7 +2841,7 @@ void RenderProcessHostImpl::UpdateProcessPriority() {
   // visible widgets -- the callers must call this function whenever we
   // transition in/out of those states.
   const bool should_background =
-      visible_widgets_ == 0 && !audio_renderer_host_->HasActiveAudio() &&
+      visible_widgets_ == 0 && !audio_streams_tracker_.has_streams() &&
       !base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableRendererBackgrounding);