Revert of Split Screen mode implementation

athena/wm/public/window_list_provider.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_PUBLIC_WINDOW_LIST_PROVIDER_H_
-#define ATHENA_WM_PUBLIC_WINDOW_LIST_PROVIDER_H_
-
-#include "athena/athena_export.h"
-#include "ui/aura/window.h"
-
-namespace athena {
-
-// Interface for an ordered list of aura::Window objects.
-class ATHENA_EXPORT WindowListProvider {
- public:
-  virtual ~WindowListProvider() {}
-
-  // Returns an ordered list of windows.
-  virtual aura::Window::Windows GetWindowList() const = 0;
-
-  // Moves the window to the front of the list.
-  virtual void MoveToFront(aura::Window* window) = 0;
-};
-
-}  // namespace athena
-
-#endif  // ATHENA_WM_PUBLIC_WINDOW_LIST_PROVIDER_H_