Make tab audible and muted states and cause available for an extension API

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index 3630835be3c192dafb7bf9034bf6b1301e8a6082..3b999316d99d75c9e5a1aa52b272b65a56157a29 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -253,6 +253,10 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   virtual void WasShown() {}
   virtual void WasHidden() {}
 
+  // These methods are invoked when there are changes related to sound.
+  virtual void TabAudible(bool isAudible) {};
+  virtual void TabMuted(bool isMuted, const std::string& cause) {};
+
   // This methods is invoked when the title of the WebContents is set. If the
   // title was explicitly set, |explicit_set| is true, otherwise the title was
   // synthesized and |explicit_set| is false.