[LayoutNG] Allow BFC block offset to differ in MaySkipLayout

r608360 enabled fragment caching when BFC block offset
changes, but r609030 disabled it when RareData exists,
probably due to merge failure.

This patch re-enables it. It recovers some of the
performance loss seen at go/layoutng-loading-perf:
https://pinpoint-dot-chromeperf.appspot.com/job/1605b070140000

Change-Id: I071fd5b4dd177245aa402718ce6f737549aa1b12
Bug: 635619
Reviewed-on: https://chromium-review.googlesource.com/c/1341741
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609694}
1 file changed