athena: Use ActivityList where appropriate, and fix AppActivity tests.

athena/activity/activity_manager_impl.h

 // Copyright 2014 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.
 
 #include "athena/activity/public/activity_manager.h"
 
 #include <vector>
 
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "ui/aura/window_observer.h"
 #include "ui/wm/public/activation_change_observer.h"
 
 namespace athena {
 
 class ActivityManagerObserver;
 
 class ActivityManagerImpl : public ActivityManager,
                             public aura::WindowObserver,
                             public aura::client::ActivationChangeObserver {
  public:
   ActivityManagerImpl();
   ~ActivityManagerImpl() override;
 
   int num_activities() const { return activities_.size(); }
 
   // ActivityManager:
   void AddActivity(Activity* activity) override;
   void RemoveActivity(Activity* activity) override;
+  ScopedActivity ReplaceActivity(Activity* to_replace,
+                                 Activity* replace_with) override;
   const ActivityList& GetActivityList() override;
   Activity* GetActivityForWindow(aura::Window* window) override;
   void AddObserver(ActivityManagerObserver* observer) override;
   void RemoveObserver(ActivityManagerObserver* observer) override;
 
  private:
+  void InitializeActivity(Activity* activity);
+  void UninitializeActivity(Activity* activity);
+
   // aura::WindowObserver:
   void OnWindowDestroying(aura::Window* window) override;
 
   // aura::client::ActivationChangeObserver:
   void OnWindowActivated(aura::Window* gained_active,
                          aura::Window* lost_active) override;
 
   std::vector<Activity*> activities_;
 
   ObserverList<ActivityManagerObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ActivityManagerImpl);
 };
 
 }  // namespace athena