diff -r 000000000000 -r 6474c204b198 layout/reftests/position-dynamic-changes/vertical/animate.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/reftests/position-dynamic-changes/vertical/animate.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,61 @@
+var currentOffset = null;
+var maxOffset = null;
+var property = "top";
+
+var rfa = null;
+if (window.requestAnimationFrame) {
+  rfa = requestAnimationFrame;
+} else if (window.mozRequestAnimationFrame) {
+  rfa = mozRequestAnimationFrame;
+} else if (window.webkitRequestAnimationFrame) {
+  rfa = webkitRequestAnimationFrame;
+} else if (window.msRequestAnimationFrame) {
+  rfa = msRequestAnimationFrame;
+} else if (window.oRequestAnimationFrame) {
+  rfa = oRequestAnimationFrame;
+}
+
+function animate(from, to, prop) {
+  currentOffset = from;
+  maxOffset = to;
+  if (prop) {
+    property = prop;
+  }
+  rfa(animateStep);
+}
+
+function animateStep() {
+  if (currentOffset <= maxOffset) {
+    document.getElementById("child").style[property] = currentOffset + "px";
+    currentOffset += 10;
+    rfa(animateStep);
+  } else {
+    document.documentElement.removeAttribute("class");
+  }
+}
+
+function toAuto(prop) {
+  if (prop) {
+    property = prop;
+  }
+  rfa(setToAuto);
+}
+
+function setToAuto() {
+  document.getElementById("child").style[property] = "auto";
+  document.documentElement.removeAttribute("class");
+}
+
+function fromAuto(to, prop) {
+  maxOffset = to;
+  if (prop) {
+    property = prop;
+  }
+  rfa(setFromAuto);
+}
+
+function setFromAuto() {
+  document.getElementById("child").style[property] = maxOffset + "px";
+  document.documentElement.removeAttribute("class");
+}
+