Be sure to repaint if we're scrolling a marquee.

I missed a case in https://chromiumcodereview.appspot.com/10989063 where repainting
was required: marquees. This patch adds a check for that case and updates the
layout test.

R=jchaffraix@chromium.org
BUG=313595

Review URL: https://codereview.chromium.org/50493016

git-svn-id: svn://svn.chromium.org/blink/trunk@161094 bbb929c8-8fbe-4397-9dbb-9b2b20218538