Restore original opacity when exiting overview

ash/common/wm/overview/scoped_transform_overview_window.h

Index: ash/common/wm/overview/scoped_transform_overview_window.h
diff --git a/ash/common/wm/overview/scoped_transform_overview_window.h b/ash/common/wm/overview/scoped_transform_overview_window.h
index 9514d34b159db83e7f5ce6a28bd918ddbad857f2..84ce30e2b6cef8d2a56c1142aebaf6549f4d9f6b 100644
--- a/ash/common/wm/overview/scoped_transform_overview_window.h
+++ b/ash/common/wm/overview/scoped_transform_overview_window.h
@@ -179,6 +179,9 @@ class ASH_EXPORT ScopedTransformOverviewWindow : public ui::EventHandler {
   // The original transform of the window before entering overview mode.
   gfx::Transform original_transform_;
 
+  // The original opacity of the window before entering overview mode.
+  float original_opacity_;
+
   // A window that holds the content for minimized window.
   std::unique_ptr<views::Widget> minimized_widget_;