[LayoutNG] Add bit in ComputedStyle for non-zero padding/margins.

This adds a bit in computed style to quickly allow us to determine if
the given style has any non-zero margin or padding.

Has about a 1-2% perf improvement with layout microbenchmarks.

Bug: 635619
Change-Id: I1f7d674c61f55730c08912e4059082abf5e511a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1492297
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639568}
14 files changed