[LayoutNG] Add some temporary CHECKs to catch crbug.com/919990

Bug: 919990
Change-Id: Icb623a7f4b353405eeb5f6f009a3a8611e1e1a3f
Reviewed-on: https://chromium-review.googlesource.com/c/1404075
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621444}
1 file changed