Attempted fix for refcount in sideloaded font path

Followup to buggy code added in http://src.chromium.org/viewvc/blink?view=rev&rev=181407 .

This code path is only used in layout tests.

TBR=eae@chromium.org
R=bungeman@chromium.org
BUG=394902

Review URL: https://codereview.chromium.org/551063002

git-svn-id: svn://svn.chromium.org/blink/trunk@181587 bbb929c8-8fbe-4397-9dbb-9b2b20218538