[layoutng] Make the layout algorithm actually compute and store positions and sizes

R=ikilpatrick@chromium.org,eae@chromium.org,glebl@chromium.org
BUG=635619
NOTRY=true

Review-Url: https://codereview.chromium.org/2231153003
Cr-Commit-Position: refs/heads/master@{#411175}
2 files changed