Enable position:sticky for <thead> and <tr> elements

third_party/WebKit/LayoutTests/fast/css/sticky/sticky-table-thead-multirow-top-expected.html

+<style>
+
+table {
+  border-collapse: collapse;
+}
+
+td, th {
+  height: 40px;
+  width: 40px;
+}
+
+th {
+  position: relative;
+  background: green;
+}
+
+.scroller {
+  overflow: auto;
+  height: 400px;
+}
+
+.padding {
+  height: 500px;
+}
+</style>
+
+<script>
+if (window.testRunner)
+  testRunner.waitUntilDone();
+
+function finishTest() {
+  document.querySelector('.scroller').scrollTop = 200;
+  if (window.testRunner)
+    testRunner.notifyDone();
+}
+
+window.addEventListener('load', function() {
+  requestAnimationFrame(function() {
+    requestAnimationFrame(finishTest);
+  });
+});
+</script>
+
+<div class="scroller">
+
+  <table>
+    <thead>
+      <tr>
+        <th style="top: 225px;" rowspan="2"></th>
+        <th style="top: 225px;" ></th>
+      </tr>
+      <tr>
+        <th style="top: 225px; background: fuchsia;"></th>
+      </tr>
+    </thead>
+    <tbody>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+      <tr><td></td><td></td></tr>
+    </tbody>
+    </table>
+
+  <div class="padding"></div>
+
+</div>