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+<!DOCTYPE html>
+<html lang="en" class="reftest-wait">
+<meta charset="utf-8">
+<title>This test fails - layerization should respect overflow:hidden clips around things with animated position</title>
+
+<style>
+
+div {
+  min-height: 50px;
+  box-model: border-box;
+}
+
+.first, .second {
+  border: 1px solid blue;
+  margin: 50px 0;
+  position: relative;
+}
+
+.border {
+  border: 1px solid black;
+}
+
+.clip {
+  height: auto;
+  overflow: hidden;
+  padding: 10px 0 20px;
+}
+
+.animated-position {
+  position: relative;
+  left: 20px;
+  margin-left: 220px;
+  width: 100px;
+  height: 100px;
+  border-color: red;
+}
+
+body {
+  margin: 0;
+  padding: 0 100px;
+  height: 3000px;
+}
+
+</style>
+
+<div class="first" reftest-assigned-layer="page-background">
+  <!--
+    This is just a regular box, it should end up in the page background layer.
+  -->
+</div>
+
+<div class="clip border">
+  <div class="border animated-position reftest-no-paint reftest-opaque-layer">
+    <!--
+      The background of .clip is uniform and opaque,
+      .animated-position should be able to pull up that background color and
+      become opaque itself.
+      However, since this clip is not created by an animated geometry root that
+      is a scrollable frame, we currently fail to recognize it, so this test
+      will fail.
+    -->
+  </div>
+</div>
+
+<div class="second" reftest-assigned-layer="page-background">
+  <!--
+    This should share a layer with .first and the page background.
+    However, since we don't recognize that .animated-position is contained in
+    a clip, .second gets its own layer above .animated-position, so this test
+    will fail.
+  -->
+</div>
+
+<script>
+
+var animatedLeft = document.querySelector(".animated-position");
+
+function doTest() {
+  animatedLeft.style.left = "-40px";
+  document.documentElement.removeAttribute("class");
+}
+
+// Layerize #animatedLeft
+animatedLeft.offsetLeft;
+animatedLeft.style.left = "40px";
+animatedLeft.offsetLeft;
+animatedLeft.style.left = "60px";
+animatedLeft.offsetLeft;
+
+document.addEventListener("MozReftestInvalidate", doTest);
+setTimeout(doTest, 200);
+
+</script>
+