Make the second argument to Element.setAttribute non-optional

LayoutTests/fast/images/style-access-during-imageChanged-style-freeze.html

 <style>
     #target[foo] { color: green; }
 </style>
 <div id="container">
     <div>
         <img src="x-invalid:" alt="Some wide text">
         <div id="target">
             This should be green, with a wide broken image above.
         </div>
     </div>
 </div>
 <div id="result"></div>
 <script>
     onload = function() {
         if (window.testRunner)
             testRunner.dumpAsText();
 
         document.body.offsetTop;
         var container = document.getElementById("container");
         container.style.display = "none";
         document.body.offsetTop;
         container.style.removeProperty("display");
         document.body.offsetTop;
         var target = document.getElementById("target");
-        target.setAttribute("foo");
+        target.setAttribute("foo", "");
         document.body.offsetTop;
         var result = document.getElementById("result");
         result.innerText = getComputedStyle(target).color === "rgb(0, 128, 0)" ? "PASS" : "FAIL";
     }
 </script>