updateForScroll method
Causes the overlay to update its rendering.
This is intended to be called when the renderObject may have changed its text metrics (e.g. because the text was scrolled).
Implementation
void updateForScroll() {
_updateSelectionOverlay();
// This method may be called due to windows metrics changes. In that case,
// non of the properties in _selectionOverlay will change, but a rebuild is
// still needed.
_selectionOverlay.markNeedsBuild();
}