[ash-md] Animates overview shield in and out

ash/common/wm/overview/window_grid.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_COMMON_WM_OVERVIEW_WINDOW_GRID_H_
 #define ASH_COMMON_WM_OVERVIEW_WINDOW_GRID_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 33 matching lines @@
 //    0, 3, 6, 1, 4, 2, 5
 // The selector is switched to the next window grid (if available) or wrapped if
 // it reaches the end of its movement sequence.
 class ASH_EXPORT WindowGrid : public WmWindowObserver {
  public:
   WindowGrid(WmWindow* root_window,
              const std::vector<WmWindow*>& window_list,
              WindowSelector* window_selector);
   ~WindowGrid() override;
 
+  // Exits overview mode, fading out the |shield_widget_| if necessary.
+  void Shutdown();
+
   // Prepares the windows in this grid for overview. This will restore all
   // minimized windows and ensure they are visible.
   void PrepareForOverview();
 
   // Positions all the windows in rows of equal height scaling each window to
   // fit that height.
   // Layout is done in 2 stages maintaining fixed MRU ordering.
   // 1. Optimal height is determined. In this stage |height| is bisected to find
   //    maximum height which still allows all the windows to fit.
   // 2. Row widths are balanced. In this stage the available width is reduced
@@ skipping 115 matching lines @@
 
   // Number of columns in the grid.
   size_t num_columns_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowGrid);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_OVERVIEW_WINDOW_GRID_H_