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

LayoutTests/fast/js/resources/image-preload-helper.js

Index: LayoutTests/fast/js/resources/image-preload-helper.js
diff --git a/LayoutTests/fast/js/resources/image-preload-helper.js b/LayoutTests/fast/js/resources/image-preload-helper.js
index 27ea17d143abaad3f1cd1f0b9144dee27b9b2804..8ce7f06b094828791f85fb1aa9d5ad523aeaea43 100644
--- a/LayoutTests/fast/js/resources/image-preload-helper.js
+++ b/LayoutTests/fast/js/resources/image-preload-helper.js
@@ -13,7 +13,7 @@ function preloadImagesFromStyle(rootNode, imageCount, onComplete, failPattern) {
     var imagesToLoad = [];
     var seenUrls = {};
     for (var i = 0; i < nodes.length; i++) {
-        var urls = nodes[i].style.cssText.split(/url\w*\(([^)]*)\)/);
+        var urls = nodes[i].style.cssText.split(/url\w*\(\"([^)]*)\"\)/);
         for (var j = 1; j < urls.length; j += 2) {
             // Attempt to convert URL to a relative path in order to have deterministic error messages.
             var url = urls[j];