Failing test for #2611 - measure div + coverGutter bug

Modified the lineWidgetChanged test to also test for #2611
Set parent width for coverGutter widgets in measure div

When using the measure div to measure a LineWidget with coverGutter: true,
set the parent's width to include the gutter. Otherwise, the widget will
be measured as if it were not meant to cover the gutter (it will be
measured at a narrower width).

Fixes #2611