dified on an ancestor of the anchor node.

var scroller;
var ancestor = document.querySelector("#ancestor");
var before = document.querySelector("#before");

function runCase(classToApply, expectSuppression) {
  // Reset.
  scroller.scrollTop = 0;
  ancestor.className = "";
  before.style.height = "";
  scroller.scrollTop = 150;

  ancestor.className = classToApply;
  before.style.height = "150px";

  var expectedTop = expectSuppression ? 150 : 200;
  assert_equals(scroller.scrollTop, expectedTop);
}

funct