Revert of Split Screen mode implementation

athena/wm/mru_window_tracker.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.
-
-#ifndef ATHENA_WM_MRU_WINDOW_TRACKER_H_
-#define ATHENA_WM_MRU_WINDOW_TRACKER_H_
-
-#include <list>
-
-#include "athena/wm/public/window_list_provider.h"
-#include "ui/aura/window_observer.h"
-
-namespace aura {
-class Window;
-}
-
-namespace athena {
-
-// Maintains a most recently used list of windows. This is used for window
-// cycling and overview mode.
-class MruWindowTracker : public WindowListProvider,
-                         public aura::WindowObserver {
- public:
-  explicit MruWindowTracker(aura::Window* container);
-  virtual ~MruWindowTracker();
-
-  // Overridden from WindowListProvider
-  virtual aura::Window::Windows GetWindowList() const OVERRIDE;
-
-  // Updates the mru_windows_ list to move |window| to the front.
-  // |window| must be the child of |container_|.
-  virtual void MoveToFront(aura::Window* window) OVERRIDE;
-
- private:
-  // Overridden from WindowObserver:
-  virtual void OnWillRemoveWindow(aura::Window* window) OVERRIDE;
-  virtual void OnWindowAdded(aura::Window* new_window) OVERRIDE;
-
-  // List of windows that have been used in the container, sorted by most
-  // recently used.
-  std::list<aura::Window*> mru_windows_;
-  aura::Window* container_;
-
-  DISALLOW_COPY_AND_ASSIGN(MruWindowTracker);
-};
-
-}  // namespace athena
-
-#endif  // ATHENA_WM_MRU_WINDOW_TRACKER_H_