The test case in this patch fails without the proper fix in the first patch
in this patch series.
In this patch two new nsIDOMWindowUtils APIs are introduced to change the
system font settins in tests. Currently the APIs work only on GTK+ platform.
Also to work the test case properly we need to open a new XUL window because we
don't propagate font changes into descendant documents yet (bug 1478212).
MozReview-Commit-ID: 4OLxEkEuF8d
--HG--
extra : rebase_source : 683e64f07c4d8820e5499d8c15b90975618559b8
61a6f8e3f2