Use DEFINE_STATIC_LOCAL for static StylePropertyShorthands.

This is just to change the initialization characteristics of the
shorthand, to see if that makes a difference for the bug.

BUG=957195

Change-Id: Icb0037219d4f080eb8e9c871f7588bb66038045e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1676708
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672471}
1 file changed