[ash-md] Fixes a bug with setting window shape to mask header in 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 e59310609a6a0650a313da80f88d86d88e4f019e..adf25f203f5157ca27fa5ead215d7f4f5d5a7f03 100644
--- a/ash/common/wm/overview/scoped_transform_overview_window.h
+++ b/ash/common/wm/overview/scoped_transform_overview_window.h
@@ -140,6 +140,10 @@ class ASH_EXPORT ScopedTransformOverviewWindow {
   // Original window shape, if it was set on a window.
   std::unique_ptr<SkRegion> original_window_shape_;
 
+  // True after the |original_window_shape_| has been set or after it has
+  // been determined that window shape was not originally set on the |window_|.
+  bool determined_original_window_shape_;
+
   // If true, the window was minimized and should be restored if the window
   // was not selected.
   bool minimized_;