Marco Trevisan authored Mar 08, 2019 and Florian Müllner committed Apr 11, 2019

Compute the source actor workarea and allocation when repositioning and keep it
cached so that we've not to calculating it again in _calculateArrowSide.

Since _calculateArrowSide only is called inside _updateFlip that is always
called just after reposition, we can be sure that the computed values are still
correct.

!435