Add support for "image-set"

third_party/WebKit/LayoutTests/fast/css/script-tests/image-set-parsing.js

-description("Test the parsing of the -webkit-image-set function.");
+description("Test the parsing of the image-set function.");
 
 var result;
 
 function testImageSetRule(description, property, rule, expectedTexts)
 {
     debug("");
     debug(description + " : " + rule);
 
     var div = document.createElement("div");
-    rule = "-webkit-image-set(" + rule + ")";
+    rule = "image-set(" + rule + ")";
     div.style[property] = rule;
     document.body.appendChild(div);
     result = div.style[property].replace(/url\("[^#]*#/g, 'url("#');
     shouldBeEqualToString("result", rule);
     document.body.removeChild(div);
 }
 
 testImageSetRule("Single value for background-image",
                 "background-image",
                 'url("#a") 1x');
@@ skipping 24 matching lines @@
 
 testImageSetRule("Single value for -webkit-mask-box-image-source",
                 "-webkit-mask-box-image-source",
                 'url("#a") 1x');
 
 testImageSetRule("Multiple values for -webkit-mask-box-image-source",
                 "-webkit-mask-box-image-source",
                 'url("#a") 1x, url("#b") 2x');
 
 successfullyParsed = true;