Handle nested position:sticky elements correctly (compositor)

third_party/WebKit/LayoutTests/compositing/overflow/composited-nested-sticky-table.html

+<style>
+body {
+  margin: 0;
+}
+
+table {
+  background: red;
+  border-collapse: collapse;
+}
+
+td, th {
+  height: 50px;
+  width: 50px;
+  padding: 0;
+}
+
+th {
+  background: green;
+}
+
+.scroller {
+  will-change: transform;
+
+  overflow: hidden; /* hide scrollbars */
+  width: 100px;
+  height: 200px;
+  outline: 2px solid black;
+}
+
+.sticky {
+  will-change: transform;
+
+  position: sticky;
+  top: 25px;
+}
+</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 class="sticky">
+      <tr class="sticky">
+        <th class="sticky"></th>
+      </tr>
+    </thead>
+    <tbody>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+      <tr><td></td></tr>
+    </tbody>
+  </table>
+</div>