Auto-rebaseline for r177329

http://src.chromium.org/viewvc/blink?view=revision&revision=177329

BUG=313447
TBR=jchaffraix@chromium.org

Review URL: https://codereview.chromium.org/363793002

git-svn-id: svn://svn.chromium.org/blink/trunk@177341 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make RenderRegionList hold RenderMultiColumnSet's

This change removes a lot of the unneeded abstraction inherited
from the RenderRegion implementation. Most of the changes are
just renaming or type tightening. One tricky bit is about
regionAtBlockOffset that had 2 implementations, one of which
was never used so it got removed. The other one is about moving
some implementation into RenderMultiColumnSet to pass the right
types to the add / remove functions.

Review URL: https://codereview.chromium.org/358973006

git-svn-id: svn://svn.chromium.org/blink/trunk@177342 bbb929c8-8fbe-4397-9dbb-9b2b20218538