Unprefix usage of -webkit-transform in tests

LayoutTests/css3/filters/nested-filter.html

 <style>
 div {
     width: 200px;
     height: 200px;
 }
 
 #div1_back {
     background-color: red;
     margin-left:40px;
     margin-top:40px;
-    -webkit-transform: rotate(-30deg);
+    transform: rotate(-30deg);
     overflow: hidden;
 }
 
 #div2_back {
     background-color: green;
-    -webkit-transform: rotate(30deg);
+    transform: rotate(30deg);
 }
 
 #div1 {
     background-color: red;
     margin-left:40px;
     margin-top:40px;
-    -webkit-transform: rotate(-30deg);
+    transform: rotate(-30deg);
     -webkit-filter: hue-rotate(100deg);
 }
 
 #div2 {
     background-color: green;
-    -webkit-transform: rotate(30deg);
+    transform: rotate(30deg);
 }
 </style>
 
 <div style="position:absolute">
     <div id="div1_back">
       <!-- This blocks should be overlaid by the second set of blocks. -->
       <div id="div2_back">
       </div>
     </div>
 </div>
 
 <div style="position:absolute">
     <div id="div1">
       <!-- This paragraph will have a filter applied. -->
       <div id="div2">
       </div>
     </div>
 </div>
 
 <script>
 if (window.testRunner)
     window.testRunner.dumpAsTextWithPixelResults();
 </script>