Handle nested position:sticky elements correctly (main thread)

third_party/WebKit/LayoutTests/fast/css/sticky/nested/sticky-nested-deep.html

Index: third_party/WebKit/LayoutTests/fast/css/sticky/nested/sticky-nested-deep.html
diff --git a/third_party/WebKit/LayoutTests/fast/css/sticky/nested/sticky-nested-deep.html b/third_party/WebKit/LayoutTests/fast/css/sticky/nested/sticky-nested-deep.html
new file mode 100644
index 0000000000000000000000000000000000000000..fc21328c26f9e1837831d6611cc4d5c48c68fb11
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/fast/css/sticky/nested/sticky-nested-deep.html
@@ -0,0 +1,81 @@
+<style>
+body {
+  margin: 0;
+}
+
+.scroller {
+  overflow: hidden; /* hide scrollbars */
+  width: 200px;
+  height: 500px;
+  outline: 2px solid black;
+}
+
+.container {
+  width: 200px;
+  height: 1000px;
+}
+
+.sticky {
+  position: sticky;
+  width: 200px;
+  top: 0;
+}
+
+.first {
+  height: 500px;
+  background: red;
+}
+
+.second {
+  height: 400px;
+  background: green;
+}
+
+.third {
+  height: 300px;
+  background: blue;
+  top: 100px;
+}
+
+.fourth {
+  height: 200px;
+  background: pink;
+  top: 100px;
+}
+
+.fifth {
+  height: 100px;
+  background: yellow;
+}
+</style>
+
+<script>
+if (window.testRunner)
+  testRunner.waitUntilDone();
+
+function finishTest() {
+  document.querySelector('.scroller').scrollTop = 400;
+  if (window.testRunner)
+    testRunner.notifyDone();
+}
+
+window.addEventListener('load', function() {
+  requestAnimationFrame(function() {
+    requestAnimationFrame(finishTest);
+  });
+});
+</script>
+
+<div class="scroller">
+  <div class="container">
+    <div class="first sticky">
+      <div class="second sticky">
+        <div class="third sticky">
+          <div class="fourth sticky">
+            <div class="fifth sticky"></div>
+          </div>
+        </div>
+      </div>
+    </div>
+  </div>
+</div>