[CrOS] Initial rough cut of alt-tab window cycling UI.

ash/wm/window_cycle_list.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 ASH_WM_WINDOW_CYCLE_LIST_H_
 #define ASH_WM_WINDOW_CYCLE_LIST_H_
 
 #include <memory>
 #include <vector>
 
 #include "ash/ash_export.h"
 #include "ash/common/wm_window_observer.h"
 #include "ash/wm/window_cycle_controller.h"
 #include "base/macros.h"
 
+namespace views {
+class Label;
+class Widget;
+}
+
 namespace ash {
 
 class ScopedShowWindow;
+class WindowCycleView;
 
 // Tracks a set of Windows that can be stepped through. This class is used by
 // the WindowCycleController.
 class ASH_EXPORT WindowCycleList : public WmWindowObserver {
  public:
   using WindowList = std::vector<WmWindow*>;
 
   explicit WindowCycleList(const WindowList& windows);
   ~WindowCycleList() override;
 
   bool empty() const { return windows_.empty(); }
 
   // Cycles to the next or previous window based on |direction|.
   void Step(WindowCycleController::Direction direction);
 
   int current_index() const { return current_index_; }
 
  private:
   friend class WindowCycleControllerTest;
   const WindowList& windows() const { return windows_; }
 
   // aura::WindowObserver overrides:
   // There is a chance a window is destroyed, for example by JS code. We need to
   // take care of that even if it is not intended for the user to close a window
   // while window cycling.
   void OnWindowDestroying(WmWindow* window) override;
 
+  // Returns true if the window list overlay should be shown.
+  bool ShouldShowUi();

[varkha, 2016/07/07 17:40:29]

Maybe keep this in ash::MaterialDesignController (or at least the flag part)?

+
   // List of weak pointers to windows to use while cycling with the keyboard.
   // List is built when the user initiates the gesture (i.e. hits alt-tab the
   // first time) and is emptied when the gesture is complete (i.e. releases the
   // alt key).
   WindowList windows_;
 
   // Current position in the |windows_|. Can be used to query selection depth,
   // i.e., the position of an active window in a global MRU ordering.
   int current_index_;
 
   // Wrapper for the window brought to the front.
   std::unique_ptr<ScopedShowWindow> showing_window_;
 
+  // The top level View for the window cycle UI. May be null if the UI is not
+  // showing.
+  WindowCycleView* cycle_view_;
+
+  // The widget that hosts the window cycle UI.
+  views::Widget* cycle_ui_widget_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowCycleList);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_WINDOW_CYCLE_LIST_H_