Add layout tests for universal overflow scrolling

LayoutTests/compositing/overflow/universal-acceleration/resources/universal-overflow.css

Index: LayoutTests/compositing/overflow/universal-acceleration/resources/universal-overflow.css
diff --git a/LayoutTests/compositing/overflow/universal-acceleration/resources/universal-overflow.css b/LayoutTests/compositing/overflow/universal-acceleration/resources/universal-overflow.css
new file mode 100644
index 0000000000000000000000000000000000000000..879cebc95dccd89ef63f5893130569cb748f3667
--- /dev/null
+++ b/LayoutTests/compositing/overflow/universal-acceleration/resources/universal-overflow.css
@@ -0,0 +1,59 @@
+body {
+    height: 2000px;
+}
+.positionFixed {
+    position: fixed;
+}
+
+.positionAbsolute {
+    position: absolute;
+}
+
+.overflow {
+    width: 300px;
+    height: 300px;
+    border: 4px solid black;
+    overflow: scroll;
+}
+
+.scrolled {
+    background-color: blue;
+    width: 250px;
+    height: 80px;
+    margin: 5px;
+    position: relative;
+}
+
+.box {
+    position: relative;
+    height: 100px;
+    width: 100px;
+    margin: 10px;
+    background-color: blue;
+}
+
+.onTop {
+    z-index: 2;
+}
+
+pre {
+    position: fixed;
+    top: 400px;
+}
+
+#positioned {
+    background-color: gray;
+    width: 200px;
+    height: 200px;
+    top: 150px;
+    left: 150px;
+}
+
+#sibling {
+    background-color: green;
+    width: 150px;
+    height: 320px;
+    top: 20px;
+    left: 20px;
+    z-index: 1;
+}