[layoutng] Add out-of-flow objects to the positioned objects map

This fixes the main remaining assertion in legacy/ng interop.

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

Review-Url: https://codereview.chromium.org/2347283002
Cr-Commit-Position: refs/heads/master@{#419311}
1 file changed