Smooth scroll animation should not override scroll anchoring update (MT)

third_party/WebKit/LayoutTests/fast/scroll-behavior/smooth-scroll/ongoing-smooth-scroll-anchors.html

+<script src="../../../resources/testharness.js"></script>
+<script src="../../../resources/testharnessreport.js"></script>
+<style>
+  body {
+    margin: 0px;
+    height: 2000px;
+    width: 2000px;
+  }
+  #changer {
+    background-color: #FF7F7F;
+    height: 10px;
+  }
+  #anchor {
+    height: 1500px;
+    background-color: #84BE6A;
+  }
+</style>
+
+<div id="changer"></div>
+<div id="anchor"></div>
+
+<script>
+  var asyncTest = async_test("Verify smooth scroll interaction with scroll anchroing");
+
+  // The element that will change in height.
+  var ch;
+
+  // Initital scroll position.
+  var initialX = 0;
+  var initialY = 10;
+  // Amount to smooth scroll by.
+  var userScrollX = 51;
+  var userScrollY = 205;
+  // Amount to change the height of the element above the viewport.
+  var changerY =  100;
+  // End position: height of ch + userScroll.
+  var endX = 51;
+  var endY = 305;
+
+  function scrollListener() {
+    if (window.scrollX == endX && window.scrollY == endY) {
+      asyncTest.done();
+      return;
+    }
+
+    if (ch.style.height != "100")
+      ch.style.height = changerY;
+  }
+
+  window.onload = function() {
+    assert_false(!window.internals, 'This test requires internals');
+    internals.runtimeFlags.scrollAnchoringEnabled = true;
+    // Turn on smooth scrolling.
+    internals.settings.setScrollAnimatorEnabled(true);
+
+    ch = document.getElementById("changer");
+    document.getElementById('anchor').scrollIntoView();
+
+    // Smooth scroll.
+    eventSender.mouseMoveTo(100, 100);
+    eventSender.continuousMouseScrollBy(-userScrollX, -userScrollY);
+
+    asyncTest.step(function() {
+      assert_equals(window.scrollX, initialX);
+      assert_equals(window.scrollY, initialY);
+    });
+
+    document.addEventListener("scroll", scrollListener);
+  }
+</script>