Bug 590415 - Mark 368020-1.html as random on WinXP, since we've clearly made it so

layout/reftests/bugs/reftest.list

@@ -588,7 +588,7 @@ fails-if(Android) != 367247-l-hidden.html 367247-l-scroll.html
 == 367612-1e.html 367612-1-ref.html
 == 367612-1f.html 367612-1-ref.html
 != 367612-1g.html 367612-1-ref.html
-== 368020-1.html 368020-1-ref.html
+random-if(/^Windows\x20NT\x205\.1/.test(http.oscpu)) == 368020-1.html 368020-1-ref.html
 == 368020-2.html 368020-2-ref.html
 fails == 368020-3.html 368020-3-ref.html # bug 368085
 fails == 368020-4.html 368020-4-ref.html # bug 368085