[layoutng] Don't cache fragments that contain abspos boxes

If we are a containing block for an abspos descendent, we can't
reuse the fragment because we don't know if the list of abspos
items has changed -- we need to let them bubble up during layout.

This is an unsatisfying solution in the long-term but should work
for now, and does fix some crashes/bugs when fragment caching is on.

Bug: 635619
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I5ea5a742ed87a8f6546a1405c5935d4d8a7686b0
Reviewed-on: https://chromium-review.googlesource.com/1015327
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556919}
1 file changed