Add audio signal to the ResourceScheduler.

content/browser/renderer_host/media/audio_renderer_host.cc

Index: content/browser/renderer_host/media/audio_renderer_host.cc
diff --git a/content/browser/renderer_host/media/audio_renderer_host.cc b/content/browser/renderer_host/media/audio_renderer_host.cc
index 8c06395eca68ecf94496c47946a26066060004d0..4d8127047c40a5c1074f6ed2287a87118a9bbc8f 100644
--- a/content/browser/renderer_host/media/audio_renderer_host.cc
+++ b/content/browser/renderer_host/media/audio_renderer_host.cc
@@ -10,6 +10,7 @@
 #include "base/metrics/histogram.h"
 #include "base/process/process.h"
 #include "content/browser/browser_main_loop.h"
+#include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/media/audio_stream_monitor.h"
 #include "content/browser/media/capture/audio_mirroring_manager.h"
 #include "content/browser/media/media_internals.h"
@@ -257,7 +258,7 @@ void AudioRendererHost::DoNotifyStreamStateChanged(int stream_id,
                                                    bool is_playing) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
-  AudioEntry* const entry = LookupById(stream_id);
+  AudioEntry* const entry(LookupById(stream_id));
   if (!entry)
     return;
 
@@ -273,20 +274,11 @@ void AudioRendererHost::DoNotifyStreamStateChanged(int stream_id,
         entry->stream_id(),
         base::Bind(&media::AudioOutputController::ReadCurrentPowerAndClip,
                    entry->controller()));
-    // TODO(dalecurtis): See about using AudioStreamMonitor instead.
-    if (!entry->playing()) {
-      entry->set_playing(true);
-      base::AtomicRefCountInc(&num_playing_streams_);
-    }
   } else {
     AudioStreamMonitor::StopMonitoringStream(
         render_process_id_, entry->render_frame_id(), entry->stream_id());
-    // TODO(dalecurtis): See about using AudioStreamMonitor instead.
-    if (entry->playing()) {
-      entry->set_playing(false);
-      base::AtomicRefCountDec(&num_playing_streams_);
-    }
   }
+  UpdateNumPlayingStreams(entry, is_playing);
 }
 
 RenderViewHost::AudioOutputControllerList
@@ -454,8 +446,7 @@ void AudioRendererHost::DeleteEntry(scoped_ptr<AudioEntry> entry) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   AudioStreamMonitor::StopMonitoringStream(
       render_process_id_, entry->render_frame_id(), entry->stream_id());
-  if (entry->playing())
-    base::AtomicRefCountDec(&num_playing_streams_);
+  UpdateNumPlayingStreams(entry.get(), false);
 }
 
 void AudioRendererHost::ReportErrorAndClose(int stream_id) {
@@ -480,6 +471,24 @@ AudioRendererHost::AudioEntry* AudioRendererHost::LookupById(int stream_id) {
   return i != audio_entries_.end() ? i->second : NULL;
 }
 
+void AudioRendererHost::UpdateNumPlayingStreams(AudioEntry* entry,
+                                                bool is_playing) {
+  bool had_active_audio = HasActiveAudio();

[mmenke, 2014/09/18 21:55:51]

This is for the entire renderer process, not a particular RenderView, no? 
That's why the AudioRendererHost has a render_process_id_, but not render view
ID.  So we actually need to go through all entries, and see if we have any
playing with the given render_view_id(Don't technically have to do this if
is_playing is true, since |entry| is such an Entry.

[aiolos (Not reviewing), 2014/09/18 22:23:11]

Ah, good catch. Dale, is there a better way to tell if a specific render view is
playing audio than iterating through the entries or adding book keeping for it?
I don't see one atm.

[DaleCurtis, 2014/09/18 22:57:38]

Ah, no there isn't.  The list shouldn't be large and you can iterate over it on
the IO thread, so it's not a huge deal.

[aiolos (Not reviewing), 2014/09/19 00:37:36]

Done.

+  if (entry->playing() != is_playing) {
+    entry->set_playing(is_playing);
+    if (is_playing) {
+      base::AtomicRefCountInc(&num_playing_streams_);
+    } else {
+      base::AtomicRefCountDec(&num_playing_streams_);
+    }
+    if (had_active_audio != HasActiveAudio()) {
+      DCHECK_CURRENTLY_ON(BrowserThread::IO);
+      ResourceDispatcherHostImpl::Get()->OnAudioRenderHostStreamStateChanged(
+          render_process_id_, entry->render_view_id(), is_playing);
+    }
+  }
+}
+
 bool AudioRendererHost::HasActiveAudio() {
   return !base::AtomicRefCountIsZero(&num_playing_streams_);
 }