Don't background processes with active audio output.

content/browser/renderer_host/media/audio_renderer_host.h

Index: content/browser/renderer_host/media/audio_renderer_host.h
diff --git a/content/browser/renderer_host/media/audio_renderer_host.h b/content/browser/renderer_host/media/audio_renderer_host.h
index 60556ee81df13c746bbfdffffd5845146eba90f1..38317ef8094fbe59d6200f16115d59fcda5e51fe 100644
--- a/content/browser/renderer_host/media/audio_renderer_host.h
+++ b/content/browser/renderer_host/media/audio_renderer_host.h
@@ -39,6 +39,7 @@
 
 #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"
@@ -84,6 +85,10 @@ class CONTENT_EXPORT AudioRendererHost : public BrowserMessageFilter {
   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;
@@ -165,6 +170,9 @@ class CONTENT_EXPORT AudioRendererHost : public BrowserMessageFilter {
   // 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);
 };