Animate the OverviewButtonTray

ash/system/status_area_widget_delegate.h

Index: ash/system/status_area_widget_delegate.h
diff --git a/ash/system/status_area_widget_delegate.h b/ash/system/status_area_widget_delegate.h
index 8dd32025a0c43cf8d1f9252224779744b1526450..740270b7a36dffd860dd849021fe3706ef869d2c 100644
--- a/ash/system/status_area_widget_delegate.h
+++ b/ash/system/status_area_widget_delegate.h
@@ -12,6 +12,11 @@
 #include "ui/views/accessible_pane_view.h"
 #include "ui/views/widget/widget_delegate.h"
 
+namespace ui {
+class Layer;
+class ScopedLayerAnimationSettings;
+}  // namespace ui
+
 namespace ash {
 class FocusCycler;
 
@@ -54,6 +59,8 @@ class ASH_EXPORT StatusAreaWidgetDelegate : public views::AccessiblePaneView,
  private:
   void UpdateWidgetSize();
 
+  ui::ScopedLayerAnimationSettings* SetupAnimationForLayer(ui::Layer* layer);
+
   const FocusCycler* focus_cycler_for_testing_;
   ShelfAlignment alignment_;