Escape the URL for the CSS url function.
Escape the URL for the CSS url function.

This fixes issues where the thumbnail on the NTP wasn't showing.

BUG=18380

TEST=Make sure that the following pages show thumbnails on the new tab
page:

  http://digg.com/?\
  http://code.google.com/p/chromium/issues/list?can=2&q=&sort=-id&colspec=ID+Stars+Pri+Area+Type+Status+Summary+Modified+Owner
  http://code.google.com/p/chromium/issues/list?can=2&q=&sort=-id&colspec=ID%20Stars%20Pri%20Area%20Type%20Status%20Summary%20Modified%20Owner

Review URL: http://codereview.chromium.org/178061

git-svn-id: http://src.chromium.org/svn/trunk/src@25081 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: ae2f722db42505b20c02023d675d599e4553b69d
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser