Bug 1392235, part 2 - Add a reftest for SVG mask reference loops. r=longsonr

layout/reftests/svg/mask-ref-loop-01.svg

@@ -0,0 +1,20 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<svg xmlns="http://www.w3.org/2000/svg">
+
+  <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=1392235 -->
+
+  <title>Test handling of simple mask reference loop</title>
+
+  <mask id="mask" x="20" y="20" width="100" height="100"
+        maskUnits="userSpaceOnUse" maskContentUnits="userSpaceOnUse">
+    <rect x="20" y="20" width="100" height="100" fill="white" mask="url(#mask)"/>
+  </mask>
+
+  <rect width="100%" height="100%" fill="lime"/>
+  <rect width="140" height="140" fill="red" mask="url(#mask)"/>
+  <rect x="20" y="20" width="100" height="100" fill="lime"/>
+
+</svg>

layout/reftests/svg/reftest.list

@@ -269,6 +269,7 @@ fuzzy-if(skiaContent,1,5) pref(svg.marker-improvements.enabled,true) == marker-o
 
 fuzzy(28,28) == mask-and-clipPath.html mask-and-clipPath-ref.html
 == mask-and-clipPath-2.svg pass.svg
+== mask-ref-loop-01.svg pass.svg
 == mask-basic-01.svg pass.svg
 fuzzy-if(skiaContent,1,10000) == mask-basic-02.svg mask-basic-02-ref.svg
 == mask-basic-03.svg pass.svg