Use precaching for more data: urls than just images.

      Also, merge the data url path with the SubstitueData path, as
they do very similar work in emulating a cache hit.

BUG=521112

Review URL: https://codereview.chromium.org/1291883002

git-svn-id: svn://svn.chromium.org/blink/trunk@200738 bbb929c8-8fbe-4397-9dbb-9b2b20218538