Import display: contents tests from csswg-test.

third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/support/util.js

+function eachDisplayContentsElementIn(document, window, callbackDo, callbackUndo) {
+  var elements = [];
+
+  document.body.offsetHeight;
+
+  // NOTE: Doing qsa('*') and getComputedStyle is just for the
+  // test's sake, since it's easier to mess it up when
+  // getComputedStyle is involved.
+  var all = document.querySelectorAll('*');
+  for (var i = 0; i < all.length; ++i) {
+    if (window.getComputedStyle(all[i]).display === "contents") {
+      callbackDo(all[i]);
+      elements.push(all[i]);
+    }
+  }
+
+  document.body.offsetHeight;
+
+  for (var i = 0; i < elements.length; ++i)
+    callbackUndo(elements[i]);
+
+  document.body.offsetHeight;
+}