[LayoutNG] Flex algorithm sizing improvements

We now set AvailableSize and PercentageResolutionSize on the
ConstraintSpace properly. And also now give the flex layout algorithm
more accurate offsets and main axis size.

Bug: 845235
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: Ia24778ffd24a6f1122e778919686a082a63d4b06
Reviewed-on: https://chromium-review.googlesource.com/1142729
Commit-Queue: David Grogan <dgrogan@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578567}
4 files changed