Add reftest for stroke-width with percentage value

layout/reftests/svg/reftest.list

@@ -5,4 +5,5 @@
 == pseudo-classes-01.svg pass.svg
 == pseudo-classes-02.svg pseudo-classes-02-ref.svg
 == rect-with-rx-or-ry-01.svg rect-with-rx-or-ry-01-ref.svg
+== stroke-width-percentage-01.svg pass.svg
 == text-in-link-01.svg text-in-link-01-ref.svg

layout/reftests/svg/stroke-width-percentage-01.svg

@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
+
+  <title>Testcase for percentage stroke-width</title>
+
+  <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=373485 -->
+
+  <rect width="100%" height="100%" fill="red"/>
+  <line y1="50%" x2="100%" y2="50%" stroke="lime" stroke-width="200%"/>
+
+</svg>