MacViews: Reattach children of native windows when they are exposed.

ui/views/cocoa/bridged_native_widget.h

Index: ui/views/cocoa/bridged_native_widget.h
diff --git a/ui/views/cocoa/bridged_native_widget.h b/ui/views/cocoa/bridged_native_widget.h
index 0bb5fd98c92dc991a4cd65c76565b575f67be260..58c60b659c0d06de71a6efbe08a2270a04c6c6d0 100644
--- a/ui/views/cocoa/bridged_native_widget.h
+++ b/ui/views/cocoa/bridged_native_widget.h
@@ -193,7 +193,8 @@ class VIEWS_EXPORT BridgedNativeWidget
   }
 
   bool target_fullscreen_state() const { return target_fullscreen_state_; }
-  bool window_visible() { return window_visible_; }
+  bool window_visible() const { return window_visible_; }
+  bool wants_to_be_visible() const { return wants_to_be_visible_; }
 
   // Overridden from ui::internal::InputMethodDelegate:
   ui::EventDispatchDetails DispatchKeyEventPostIME(ui::KeyEvent* key) override;