Don't require getPropertyCSSValue in fast/css tests

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

 description("Test the parsing of the -webkit-image-set function.");
 
 // These have to be global for the test helpers to see them.
 var cssRule;
 
-function testInvalidImageSet(description, property, rule)
+function testInvalidImageSet(description, rule)
 {
     debug("");
     debug(description + " : " + rule);
 
     var div = document.createElement("div");
-    div.setAttribute("style", property + ": -webkit-image-set(" + rule + ")");
+    div.style.backgroundImage = "-webkit-image-set(" + rule + ")";
     document.body.appendChild(div);
 
-    cssRule = div.style.getPropertyCSSValue(property);
-    shouldBe("cssRule", "null");
+    cssRule = div.style.backgroundImage;
+    shouldBeEmptyString("cssRule");
 
     document.body.removeChild(div);
 }
 
-testInvalidImageSet("Too many url parameters", "background-image", "url(#a #b)");
-testInvalidImageSet("No x", "background-image", "url('#a') 1");
-testInvalidImageSet("No comma", "background-image", "url('#a') 1x url('#b') 2x");
-testInvalidImageSet("Too many scale factor parameters", "background-image", "url('#a') 1x 2x");
-testInvalidImageSet("Scale factor is 0", "background-image", "url('#a') 0x");
-testInvalidImageSet("No url function", "background-image", "'#a' 1x");
+testInvalidImageSet("Too many url parameters", "url(#a #b)");
+testInvalidImageSet("No x", "url('#a') 1");
+testInvalidImageSet("No comma", "url('#a') 1x url('#b') 2x");
+testInvalidImageSet("Too many scale factor parameters", "url('#a') 1x 2x");
+testInvalidImageSet("Scale factor is 0", "url('#a') 0x");
+testInvalidImageSet("No url function", "'#a' 1x");
 
 successfullyParsed = true;