Don't background processes with active audio output.

content/browser/renderer_host/media/audio_renderer_host.h

 // 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.
 //
 // AudioRendererHost serves audio related requests from AudioRenderer which
 // lives inside the render process and provide access to audio hardware.
 //
 // This class is owned by BrowserRenderProcessHost, and instantiated on UI
 // thread, but all other operations and method calls happen on IO thread, so we
 // need to be extra careful about the lifetime of this object. AudioManager is a
@@ skipping 21 matching lines @@
 //      |         CloseStream >         |
 //      v                               v
 
 // A SyncSocket pair is used to signal buffer readiness between processes.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_RENDERER_HOST_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_RENDERER_HOST_H_
 
 #include <map>
 
+#include "base/atomic_ref_count.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/process/process.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_message_filter.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/render_view_host.h"
 #include "media/audio/audio_io.h"
@@ skipping 25 matching lines @@
   // Calls |callback| with the list of AudioOutputControllers for this object.
   void GetOutputControllers(
       int render_view_id,
       const RenderViewHost::GetAudioOutputControllersCallback& callback) const;
 
   // BrowserMessageFilter implementation.
   virtual void OnChannelClosing() OVERRIDE;
   virtual void OnDestruct() const OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
+  // Returns true if any streams managed by this host are actively playing.  Can
+  // be called from any thread.
+  bool HasActiveAudio();
+
  private:
   friend class AudioRendererHostTest;
   friend class BrowserThread;
   friend class base::DeleteHelper<AudioRendererHost>;
   friend class MockAudioRendererHost;
   friend class TestAudioRendererHost;
   FRIEND_TEST_ALL_PREFIXES(AudioRendererHostTest, CreateMockStream);
   FRIEND_TEST_ALL_PREFIXES(AudioRendererHostTest, MockStreamDataConversation);
 
   class AudioEntry;
@@ skipping 61 matching lines @@
   media::AudioManager* const audio_manager_;
   AudioMirroringManager* const mirroring_manager_;
   scoped_ptr<media::AudioLog> audio_log_;
 
   // Used to access to AudioInputDeviceManager.
   MediaStreamManager* media_stream_manager_;
 
   // A map of stream IDs to audio sources.
   AudioEntryMap audio_entries_;
 
+  // The number of streams in the playing state.
+  base::AtomicRefCount num_playing_streams_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioRendererHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_RENDERER_HOST_H_