Fixed the audio backgrounding bug

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 dddeee21626a31f30aff5b4f749c396fcd5024b8..12fee35c93cf144117701e414d1c6afb999ed7b2 100644
--- a/content/browser/renderer_host/media/audio_renderer_host.cc
+++ b/content/browser/renderer_host/media/audio_renderer_host.cc
@@ -651,11 +651,33 @@ void AudioRendererHost::UpdateNumPlayingStreams(AudioEntry* entry,
         !RenderFrameHasActiveAudio(entry->render_frame_id());
     entry->set_playing(true);
     base::AtomicRefCountInc(&num_playing_streams_);
+
+    // If it's the first audio stream to start for this renderer.
+    if (base::AtomicRefCountIsOne(&num_playing_streams_)) {
+      RenderProcessHost* render_process_host =
+          RenderProcessHost::FromID(render_process_id_);
+
+      BrowserThread::PostTask(
+          BrowserThread::UI, FROM_HERE,
+          base::Bind(&RenderProcessHost::AudioStarted,
+                     base::Unretained(render_process_host)));
+    }
   } else {
     entry->set_playing(false);
     should_alert_resource_scheduler =
         !RenderFrameHasActiveAudio(entry->render_frame_id());
     base::AtomicRefCountDec(&num_playing_streams_);
+
+    // If it was the last audio stream playing for this renderer.
+    if (base::AtomicRefCountIsZero(&num_playing_streams_)) {

[DaleCurtis, 2015/06/29 22:21:40]

You can use the result of AtomicRefCountDec instead of doing a whole new atomic
operation.

[sebsg, 2015/06/29 22:35:00]

Done.

+      RenderProcessHost* render_process_host =
+          RenderProcessHost::FromID(render_process_id_);
+
+      BrowserThread::PostTask(
+          BrowserThread::UI, FROM_HERE,
+          base::Bind(&RenderProcessHost::AudioStopped,
+                     base::Unretained(render_process_host)));
+    }
   }
 
   if (should_alert_resource_scheduler && ResourceDispatcherHostImpl::Get()) {