Convert fast/multicol/client-rects.html to reftest.

 * Use standards mode.
 * Use inline-block to make all the content fit in content_shell.
 * Use 'margin: 0' for input=range to simplify the reference file.
 * Use a solid color rather than opacity (to deal with the rogue extra
   "outline" drawn for alt-imgs).

R=mstensho@opera.com
BUG=386567

Review URL: https://codereview.chromium.org/667693002

git-svn-id: svn://svn.chromium.org/blink/trunk@184128 bbb929c8-8fbe-4397-9dbb-9b2b20218538