can-close? (augments, and augmentable only) in frame:editor-mixin

Called just before the window might be closed (e.g., by the window manager). If #f is returned, the window is not closed, otherwise on-close is called and the window is closed (i.e., the window is hidden, like calling show with #f).

This method is not called by show .

• (send a-frame:editor-mixin can-close? void

  Calls the editor:basic<%>'s method can-close?.