commit c156dc3763b001a5327ae9453222ae73bd2520e0
author Morten Stenshorne <mstensho@chromium.org> Tue Aug 29 23:42:38 2023
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Aug 29 23:42:38 2023
tree cec09136ad8c61a037319a46a712ff637949c2db
parent 4c56ce302dcacd384784e69a6fe553cf26138e76

Avoid O(n^2) in layout of many fragmentainers.

We only need to know the stitched LayoutBox size of all the fragments
combined when we're done with the last fragment, so avoid going through
every fragment for every fragment. We used to end up in
LayoutBox::ComputeSize() (which loops through every fragment) for every
fragment.

This improves perf_tests/layout/multicol/tall-content-short-columns.html
performance from 0.77 runs per second to 1.15 runs per second. That's
about 50% faster, which isn't a lot, but there are other O(n^2) issues
which play a bigger role here, especially during pre-paint. We don't
have a separate test for just layout, but that shouldn't be necessary,
either.

Bug: 1476776
Change-Id: Ie9ca7ea5b6decfd3c775217548bb4482bdb5cfec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4821786
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1189824}