Make sure <url>s are being serialized according to spec

third_party/WebKit/LayoutTests/svg/custom/marker-getPropertyValue.svg

 <?xml version="1.0" encoding="UTF-8"?>
 <svg xmlns="http://www.w3.org/2000/svg" onload="runTest()">
   <script type="text/ecmascript"><![CDATA[
 
     function expect(string, val) {
       var b = string == val;
       var message = (string + "") + " " +  (b ? "PASSED" : "FAILED (actual: '" + string + "' expected: '" + val + "')");
       var txt = document.createElementNS("http://www.w3.org/2000/svg", "text");
       var textNode = document.createTextNode(message);
       txt.appendChild(textNode);
       document.rootElement.appendChild(txt);
     }
 
     function runTest() {
       if (window.testRunner)
         testRunner.dumpAsText();
 
       var e = document.getElementById("rect");
-      expect(e.style.getPropertyValue("marker"), "url(#test)");
+      expect(e.style.getPropertyValue("marker"), 'url("#test")');
     }
   ]]></script>  
-    <rect visibility="hidden" width="100" height="100" id="rect" style="marker: url(#test)"/>
+    <rect visibility="hidden" width="100" height="100" id="rect" style='marker: url("#test")'/>
 </svg>