Fixed the audio backgrounding bug

content/public/browser/render_process_host.h

Index: content/public/browser/render_process_host.h
diff --git a/content/public/browser/render_process_host.h b/content/public/browser/render_process_host.h
index 64410e731a42b924e9c3e250463eee924b635ee1..aba3a82759549f1efcb0b2f84c52818adb0389a9 100644
--- a/content/public/browser/render_process_host.h
+++ b/content/public/browser/render_process_host.h
@@ -100,6 +100,14 @@ class CONTENT_EXPORT RenderProcessHost : public IPC::Sender,
   virtual void WidgetHidden() = 0;
   virtual int VisibleWidgetCount() const = 0;
 
+  // Called when no audio streams remain for this render process host. Must be
+  // called on the UI thread.

[ncarter (slow), 2015/07/06 21:53:57]

All the methods of this class must be called on the UI thread, so you don't need
these comments.

[sebsg, 2015/08/02 16:44:23]

Done.

+  virtual void AudioStopped() = 0;
+
+  // Called when a first audio stream has started for this render process host.
+  // Must be called on the UI thread.
+  virtual void AudioStarted() = 0;
+
   // Indicates whether the current RenderProcessHost is exclusively hosting
   // guest RenderFrames. Not all guest RenderFrames are created equal.  A guest,
   // as indicated by BrowserPluginGuest::IsGuest, may coexist with other