Clean up the way layout tests force elements to opt in/out of composited scrolling.

LayoutTests/compositing/overflow/automatically-opt-into-composited-scrolling.html

Index: LayoutTests/compositing/overflow/automatically-opt-into-composited-scrolling.html
diff --git a/LayoutTests/compositing/overflow/automatically-opt-into-composited-scrolling.html b/LayoutTests/compositing/overflow/automatically-opt-into-composited-scrolling.html
index 8c5a37e8ad2b0a77a0bd9bec18a6110aeac8a369..91c694a7aae2ff57f52e3ff509a64bf8e85a1c9c 100644
--- a/LayoutTests/compositing/overflow/automatically-opt-into-composited-scrolling.html
+++ b/LayoutTests/compositing/overflow/automatically-opt-into-composited-scrolling.html
@@ -53,12 +53,17 @@
   </style>
   <script src="resources/automatically-opt-into-composited-scrolling.js"></script>
   <script>
+    if (window.internals)
+      window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabledMode(
+          window.internals.settings.AcceleratedCompositingForOverflowScrollEnabled);
+
     function testPermutation(count, ordering, hasPositionedAncestor, containerIsPositioned)
     {
       if (!window.internals)
         return;
 
       var container = document.getElementById('container');
+      var containerOptedIn = didOptIn(container);
 
       // Below, when we set webkitTransform to '', we want that to force an
       // immediate, synchronous style recalculation. Querying the
@@ -79,17 +84,21 @@
       // composited. To ensure that we perform the full style recalc, we need to
       // change a style property so the style is dirty, and force the style to
       // be cleaned with document.body.offsetTop (inside getStackingOrder()).
-      window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabled(false);
+      window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabledMode(
+          window.internals.settings.AcceleratedCompositingForOverflowScrollDisabled);
       container.style.webkitTransform = '';
 
       var oldStackingOrder = getStackingOrder(container);
 
-      // force to promote.
-      window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabled(true);
+      window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabledMode(
+          window.internals.settings.AcceleratedCompositingForOverflowScrollAlwaysOn);

[Julien - ping for review, 2013/05/13 20:48:56]

This is actually a change in behavior in the test as
setAcceleratedCompositingForOverflowScrollEnabled(true) maps to
setAcceleratedCompositingForOverflowScrollEnabledMode(AcceleratedCompositingForOverflowScrollEnabled).

I would like an explanation in the change description and possibly the test as
to why this is required.

       container.style.webkitTransform = 'translateZ(0px)';
 
       var newStackingOrder = getStackingOrder(container);
 
+      window.internals.settings.setAcceleratedCompositingForOverflowScrollEnabledMode(
+          window.internals.settings.AcceleratedCompositingForOverflowScrollEnabled);
+
       var shouldOptIn = oldStackingOrder.length === newStackingOrder.length;
       for (var i = 0; i < oldStackingOrder.length; ++i) {
         if (oldStackingOrder[i] !== newStackingOrder[i]) {
@@ -99,7 +108,7 @@
       }
 
       container.style.webkitTransform = '';
-      if (shouldOptIn !== didOptIn(container)) {
+      if (shouldOptIn !== containerOptedIn) {
         if (shouldOptIn)
           write("FAIL - should've automatically opted in but didn't " + count);
         else