[LayoutNG] Don't crash when flex has out of flow children

Static position isn't calculated in this patch but at least we now
layout the out of flow children instead of crashing.

Bug: 845235
Change-Id: I96ca19179de35624978fb28aade2c02a4ce5cb7b
Reviewed-on: https://chromium-review.googlesource.com/c/1379109
Reviewed-by: Aleks Totic <atotic@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: David Grogan <dgrogan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617592}
3 files changed