Remove updatePaintingInfoForFragments() and per-fragment shouldPaintContent flag.

It seems that all it did was to erroneously make us skip fragments. It
intersected with layer bounds, which don't include layer overflow. Before
we create the fragments in RenderMultiColumnSet, we carefully intersect
with everything relevant anyway. So rather than fixing the buggy code,
just remove it.

This means that there's no need for a per-fragment shouldPaintContent flag.
anymore.

BUG=359877

Review URL: https://codereview.chromium.org/666493002

git-svn-id: svn://svn.chromium.org/blink/trunk@184562 bbb929c8-8fbe-4397-9dbb-9b2b20218538