Delay parent repaint when changing scroll offset.

If we change the scroll offset of a RenderLayerScrollableArea we may need
to repaint the parent. If we're current using enableRepaintAfterLayout, and
we are in a layout, we mark the parent as needing a full repaint instead of
doing the repaint immediately.

BUG=310398

Review URL: https://codereview.chromium.org/139303017

git-svn-id: svn://svn.chromium.org/blink/trunk@165336 bbb929c8-8fbe-4397-9dbb-9b2b20218538