If a <details> is a multi-column container, and has a column-span child
inside, aFrame can be ColumnSetWrapper or column-span-wrapper frame (due
to GetInsertionPrevSibling()'s modification). The latter case is handled
by "Situation #5 in WipeContainingBlock(), and can be reproduced by
changing <article> tag to <details> in
testing/web-platform/tests/css/css-multicol/multicol-span-all-dynamic-add-005.html

In any case, aFrame might end up in a frame generated by the <details>
element. I feel the assertion to check frame types might not be very
useful. Let's remove it.