RenderBlockFlow causing repaints during layout.

This CL updates RenderBlockFlow to not repaintOverflow() if we are currently
in repaintAfterLayout mode. The repaintOverflow() will be down when we do
the full repaintTree call instead of immediately.

BUG=310398

Review URL: https://codereview.chromium.org/111713005

git-svn-id: svn://svn.chromium.org/blink/trunk@163559 bbb929c8-8fbe-4397-9dbb-9b2b20218538