Introduce paintFragmentWithPhase(), to simplify paint*ForFragments().

There was some ~duplicated code in those methods, pertaining to clipping
and setting up a PaintInfo and calling renderer::paint().

R=chrishtr@chromium.org

Review URL: https://codereview.chromium.org/704753002

git-svn-id: svn://svn.chromium.org/blink/trunk@184936 bbb929c8-8fbe-4397-9dbb-9b2b20218538