[LayoutNG] Split apart storage for AvailableSize and PercentageSize.

Additionally removes ContainerSize.

We've got lots of small corner cases which we aren't handling correctly
in ng_length_utils (i.e. orthoganal writing mode %-resolution). But
will fix these in follow-up patch.

BUG=635619

Review-Url: https://codereview.chromium.org/2483683003
Cr-Commit-Position: refs/heads/master@{#430434}
17 files changed