Handle nested position:sticky elements correctly (compositor)

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

Index: third_party/WebKit/LayoutTests/compositing/overflow/composited-nested-sticky-top.html
diff --git a/third_party/WebKit/LayoutTests/compositing/overflow/composited-nested-sticky-top.html b/third_party/WebKit/LayoutTests/compositing/overflow/composited-nested-sticky-top.html
new file mode 100644
index 0000000000000000000000000000000000000000..92180d809d18a9a32ba729ed1d68a1fce063a245
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/compositing/overflow/composited-nested-sticky-top.html
@@ -0,0 +1,92 @@
+<style>
+body {
+  margin: 0;
+}
+
+.group {
+  display: inline-block;
+  position: relative;
+  width: 250px;
+  height: 350px;
+}
+
+.scroller {
+  will-change: transform;
+
+  overflow: hidden; /* hide scrollbars */
+  width: 200px;
+  height: 350px;
+  outline: 2px solid black;
+}
+
+.container {
+  width: 200px;
+  height: 700px;
+}
+
+.outerSticky {
+  will-change: transform;
+
+  position: sticky;
+  background-color: green;
+  width: 200px;
+  height: 200px;
+}
+
+.innerSticky {
+  will-change: transform;
+
+  position: sticky;
+  background-color: red;
+  width: 200px;
+  height: 100px;
+}
+</style>
+
+<script>
+if (window.testRunner)
+  testRunner.waitUntilDone();
+
+function finishTest() {
+  for (const scroller of document.querySelectorAll('.scroller')) {
+    scroller.scrollTop = 200;
+  }
+  if (window.testRunner)
+    testRunner.notifyDone();
+}
+
+window.addEventListener('load', function() {
+  requestAnimationFrame(function() {
+    requestAnimationFrame(finishTest);
+  });
+});
+</script>
+<div class="group">
+  <div class="scroller">
+    <div class="container">
+      <div class="outerSticky" style="top: 50px;">
+        <div class="innerSticky" style="top: 50px;"></div>
+      </div>
+    </div>
+  </div>
+</div>
+
+<div class="group">
+  <div class="scroller">
+    <div class="container">
+      <div class="outerSticky" style="top: 50px;">
+        <div class="innerSticky" style="top: 100px;"></div>
+      </div>
+    </div>
+  </div>
+</div>
+
+<div class="group">
+  <div class="scroller">
+    <div class="container">
+      <div class="outerSticky" style="top: 50px;">
+        <div class="innerSticky" style="top: 300px;"></div>
+      </div>
+    </div>
+  </div>
+</div>