Fix for undesired audio blip when closing a muted tab.

content/browser/renderer_host/media/audio_renderer_host.cc

 // Copyright (c) 2012 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/audio_renderer_host.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/memory/shared_memory.h"
@@ skipping 421 matching lines @@
 
   // Prevent oustanding callbacks from attempting to close/delete the same
   // AudioEntry twice.
   AudioEntryMap::iterator i = audio_entries_.find(stream_id);
   if (i == audio_entries_.end())
     return;
   scoped_ptr<AudioEntry> entry(i->second);
   audio_entries_.erase(i);
 
   media::AudioOutputController* const controller = entry->controller();
-  if (mirroring_manager_)
-    mirroring_manager_->RemoveDiverter(controller);
   controller->Close(
       base::Bind(&AudioRendererHost::DeleteEntry, this, base::Passed(&entry)));
   audio_log_->OnClosed(stream_id);
 }
 
 void AudioRendererHost::DeleteEntry(scoped_ptr<AudioEntry> entry) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  // De-register the controller from the AudioMirroringManager now that the
+  // controller has closed the AudioOutputStream and shut itself down.  This
+  // ensures that calling RemoveDiverter() here won't trigger the controller to
+  // re-start the default AudioOutputStream and cause a brief audio blip to come
+  // out the user's speakers.  http://crbug.com/474432
+  if (mirroring_manager_)
+    mirroring_manager_->RemoveDiverter(entry->controller());
+
   AudioStreamMonitor::StopMonitoringStream(
       render_process_id_, entry->render_frame_id(), entry->stream_id());
   UpdateNumPlayingStreams(entry.get(), false);
 }
 
 void AudioRendererHost::ReportErrorAndClose(int stream_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   // Make sure this isn't a stray callback executing after the stream has been
   // closed, so error notifications aren't sent after clients believe the stream
@@ skipping 52 matching lines @@
        it != audio_entries_.end();
        ++it) {
     AudioEntry* entry = it->second;
     if (entry->render_frame_id() == render_frame_id && entry->playing())
       return true;
   }
   return false;
 }
 
 }  // namespace content