Clear the dockpanel overlay if a descendant will handle the drop.
Clear the dockpanel overlay if a descendant will handle the drop.

Our heuristic is that if a descendant will handle the drop, it will handle drag over events and they won’t bubble up to us. We hide the overlay asynchronously, so the hide will be cancelled if a p-dragover event bubbles up to us.
blink1073/phosphor,phosphorjs/phosphor,phosphorjs/phosphor,blink1073/phosphor