Fallback to using screen width and height causing problems

[paour]

I haven't had time to fully investigate why DragDropGrid.acknowledgeHeightSize() was being called with a 0 height, but the fallback to using the screen dimensions is probably not the way to go: it will always generate a view that is too tall, and for multi-pane layouts it will be too wide as well.

[paour]

Using this solution may resolve this issue: wait for the parent to be laid out, then get its size.