Handle auto-positioned out-of-flow objects inside multicol containers correctly.

We used to get it all wrong for out-of-flow children of multicol containers
whose containing block were on the outside of the multicol container. Those
do not live in the flow thread coordinate space, so we have to convert their
location to visual coordinates.

BUG=291616

Review-Url: https://codereview.chromium.org/2250713002
Cr-Commit-Position: refs/heads/master@{#412375}
20 files changed