Fix "modal isn't modal in multi displays" issue

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index 535f7d1e4840381c0d3c268aea4320dc7cb9e7e7..1b19fc6bd93d3a049c1545b00db93fc1966e0064 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -168,6 +168,9 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   void ShowContextMenu(const gfx::Point& location_in_screen,
                        ui::MenuSourceType source_type);
 
+  // True if the window can receive events on this root window.
+  bool CanWindowReceiveEvents(aura::Window* window);
+
   // Returns the layout-manager for the appropriate modal-container. If the
   // window is inside the lockscreen modal container, then the layout manager
   // for that is returned. Otherwise the layout manager for the default modal