Add layout tests for universal overflow scrolling

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

+if (window.internals) {
+    window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabled(true);
+//    internals.setUniversalAcceleratedCompositingForOverflowScrollEnabled(true);

[Julien - ping for review, 2013/08/21 01:34:40]

This line is probably unneeded :)

[Ian Vollick, 2013/08/23 15:02:40]

lol. Done.

+}
+
+var isFixedPositioned = true;
+var isContainingBlock = true;
+var hasSibling = true;
+var hasGrandchildren = true;

[Julien - ping for review, 2013/08/21 01:34:40]

These variables are just magical and make it hard to understand what's going on
(the tests are overriding them).

One way to change that is to wrap the whole code into a function:

function setUpTest(parameters) {
var isFixedPositioned = parameters.isFixedPositioned || false;

}

This would be called inside your HTML and would expose what is needed.

[Ian Vollick, 2013/08/23 15:02:40]

I've rearranged things a bunch and come up with something similar to what you've
suggested that's hopefully a little less magical. We explicitly ask for a
default set of parameters (so it's both clear to readers where to look to find
out what all the parameters are and so that it's easy to add a new parameter
without updating all tests), update it for the particular test and then
explicitly call doTest(parameters). WDYT?

+
+function addDomElement(elementType, className, id, parent, description, indent)
+{
+    var element = document.createElement(elementType);
+    element.setAttribute("class", className);
+    element.setAttribute("id", id);
+    if (parent === "body")
+        document.body.appendChild(element);
+    else
+        document.getElementById(parent).appendChild(element);
+
+    if (elementType === "div") {
+        for (var i = 0; i < indent; ++i)
+            description.push("  ");
+        description.push("+ ");
+        description.push(id);
+        if (className) {
+            description.push(", class: ");
+            description.push(className);
+        }
+        description.push("\n");
+    } else {
+        element.innerHTML = description.join("");
+    }
+}
+
+function buildDom(description, indent)
+{
+    var parentElement = "body";
+    if (hasSibling) {
+        addDomElement("div", "", "ancestor", "body", description, indent);
+        indent++;
+        addDomElement("div", "positionFixed", "sibling", "ancestor", description, indent);
+        parentElement = "ancestor";
+    }
+
+    var overflowClass = isContainingBlock
+        ? "positionAbsolute overflow"
+        : "overflow";
+
+    addDomElement("div", overflowClass, "container", parentElement, description, indent);
+    indent++;
+
+    parentElement = "container";
+    if (hasGrandchildren) {
+        addDomElement("div", "", "scrollingContainer", parentElement, description, indent);
+        indent++;
+        parentElement = "scrollingContainer";
+    }
+
+    positionedClass = isFixedPositioned ? "positionFixed" : "positionAbsolute";
+
+    addDomElement("div", positionedClass, "positioned", parentElement, description, indent);
+
+    for (var i = 0; i < 5; ++i) {
+        var scrolledClass = "scrolled";
+        if ((i % 2) == 0) {

[Julien - ping for review, 2013/08/21 01:34:40]

We usually don't put curly braces for single line statement.

[Ian Vollick, 2013/08/23 15:02:40]

Done.

+            scrolledClass += " onTop";
+        }
+        addDomElement("div", scrolledClass, "scrolled", parentElement, description, indent);
+    }
+}
+
+function doTest() {
+    var description = ["This test constructs the following tree:\n"];
+    var indent = 0;
+    buildDom(description, indent)
+
+    if (!window.internals) {
+        addDomElement("pre", "", "console", "body", description, indent);
+        var pre = document.getElementById("console");
+        pre.innerHTML += "\nWe then check that scrolling is accelerated.";
+    } else {
+      testRunner.dumpAsText(true);
+
+      var container = document.getElementById("container");
+      container.scrollTop = container.scrollHeight - container.clientHeight;
+
+      var layerTreeAsText = internals.layerTreeAsText(document);
+
+      addDomElement("pre", "", "console", "body", description, indent);
+      var pre = document.getElementById("console");
+      pre.style.left = "-80000px";
+      pre.innerHTML = layerTreeAsText;
+    }
+}