[LayoutNG] Remove ICB size from NGConstraintSpace.

This removes another 2xLayoutUnits on the NGConstraintSpace.
This should have no behaviour change.

Bug: 635619
Change-Id: I765139563ffc9b167fefffe16ed3674c1db5dbf9
Reviewed-on: https://chromium-review.googlesource.com/c/1340585
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610900}
24 files changed