[ash-md] Improves smoothness with many windows in overview

ash/common/wm/overview/window_selector_item.h

 // Copyright 2013 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_SELECTOR_ITEM_H_
 #define ASH_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_ITEM_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 94 matching lines @@
   // enabled.
   void SendAccessibleSelectionEvent();
 
   // Closes |transform_window_|.
   void CloseWindow();
 
   // Sets if the item is dimmed in the overview. Changing the value will also
   // change the visibility of the transform windows.
   void SetDimmed(bool dimmed);
   bool dimmed() const { return dimmed_; }
+  void set_hide_header(bool hide_header) { hide_header_ = hide_header; }
 
   const gfx::Rect& target_bounds() const { return target_bounds_; }
 
   // views::ButtonListener:
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
   // WmWindowObserver:
   void OnWindowDestroying(WmWindow* window) override;
   void OnWindowTitleChanged(WmWindow* window) override;
 
@@ skipping 40 matching lines @@
   ScopedTransformOverviewWindow transform_window_;
 
   // The target bounds this selector item is fit within.
   gfx::Rect target_bounds_;
 
   // True if running SetItemBounds. This prevents recursive calls resulting from
   // the bounds update when calling ::wm::RecreateWindowLayers to copy
   // a window layer for display on another monitor.
   bool in_bounds_update_;
 
+  // If true, mask the original window header while in overview. This has
+  // performance implications so it can be disabled when there are many windows.
+  bool hide_header_;
+
   // Label displaying its name (active tab for tabbed windows).
   // With Material Design this Widget owns |caption_container_view_| and is
   // shown above the |transform_window_|.
   // Otherwise it is shown under the window.
   std::unique_ptr<views::Widget> window_label_;
 
   // Shadow around the item in overview.
   std::unique_ptr<::wm::Shadow> shadow_;
 
   // Label background widget used to fade in opacity when moving selection.
@@ skipping 17 matching lines @@
   // Pointer to the WindowSelector that owns the WindowGrid containing |this|.
   // Guaranteed to be non-null for the lifetime of |this|.
   WindowSelector* window_selector_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowSelectorItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_ITEM_H_