Decoupling visibility states from webcontent, adding visibility management in ResourceManager

athena/activity/public/activity.h

Index: athena/activity/public/activity.h
diff --git a/athena/activity/public/activity.h b/athena/activity/public/activity.h
index 041449b6721cadd043ada2540febd38746be5470..231897ccbe6221a1a0aa7bd4396d4b9a7313cecd 100644
--- a/athena/activity/public/activity.h
+++ b/athena/activity/public/activity.h
@@ -60,7 +60,8 @@ class ATHENA_EXPORT Activity {
     ACTIVITY_MEDIA_STATE_AUDIO_PLAYING  // Audible audio is playing in activity.
   };
 
-  virtual ~Activity();
+  // Close an activity.
+  static void CloseActivity(Activity* activity);
 
   // The Activity retains ownership of the returned view-model.
   virtual ActivityViewModel* GetActivityViewModel() = 0;
@@ -80,6 +81,9 @@ class ATHENA_EXPORT Activity {
   // Returns the window for the activity. This can be used to determine the
   // stacking order of this activity against others.
   virtual aura::Window* GetWindow() = 0;
+
+ protected:
+  virtual ~Activity() {}
 };
 
 }  // namespace athena