Stop RenderLayerScrollableArea from repainting during layout.

Currently the RenderLayerScrollableArea will repaint its containing box
during layout when it knows the scrollbars have changed. We don't need to do
this repaint in the case of repaintAfterLayout as long as we record the
layout rects for the containing box.

BUG=310398

Review URL: https://codereview.chromium.org/136883009

git-svn-id: svn://svn.chromium.org/blink/trunk@165167 bbb929c8-8fbe-4397-9dbb-9b2b20218538