Bug 1476724 - Mark default-style/button.html as fuzzy on debug linux. r=jrmuizel

MozReview-Commit-ID: CEhtvTB0VXa

--HG--
extra : rebase_source : 30eb9731c96e609ea529eebcf7d376e4e380723b

layout/reftests/css-invalid/default-style/reftest.list

@@ -1,5 +1,5 @@
 == input.html input-ref.html
-== button.html button-ref.html
+fuzzy-if(isDebugBuild&&gtkWidget,1,1) == button.html button-ref.html
 == textarea.html textarea-ref.html
 == select.html select-ref.html
 == fieldset.html fieldset-ref.html