[css-flexbox] freezeInflexibleItems has to skip out-of-flow boxes

Out-of-flow items should not be frozen. This would have problematic
effects when they have flex-grow/flex-shrink set because freezing
them would subtract them from our flex-grow/shrink total without
having been added.

This also adds some DCHECKs.

R=eae@chromium.org,dgrogan@chromium.org
BUG=628072

Review-Url: https://codereview.chromium.org/2146603007
Cr-Commit-Position: refs/heads/master@{#405608}
2 files changed