NOT FOR REVIEW - Update comp-scrolling state at a well defined point in the pipeline.

LayoutTests/compositing/overflow/resources/automatically-opt-into-composited-scrolling.js

 var debugMode = false;
 
 if (window.testRunner)
   testRunner.dumpAsText();
 
 function write(str)
 {
   var pre = document.getElementById('console');
   var text = document.createTextNode(str + '\n');
   pre.appendChild(text);
@@ skipping 139 matching lines @@
 
         // We want the first descendant succeeding us in the ordering to get
         // z-index: 0.
         if (numElementsWithZIndexZero === 3) {
           if (firstChildIndex > containerIndex)
             ordering[firstChildIndex].style.zIndex = '0';
           else
             ordering[secondChildIndex].style.zIndex = '0';
         }
 
+        if (debugMode) {
+          write('permutationIteration: ' + permutationIteration);
+          write('hasPositionedAncestor ' + hasPositionedAncestor);
+          write('ancestor, z-index: ' + ancestor.style.zIndex + ', position: ' + ancestor.style.position + ', display: ' + ancestor.style.display);
+          write('predecessor, z-index: ' + predecessor.style.zIndex + ', position: ' + predecessor.style.position + ', display: ' + predecessor.style.display);
+          write('successor, z-index: ' + successor.style.zIndex + ', position: ' + successor.style.position + ', display: ' + successor.style.display);
+          write('firstChild, z-index: ' + firstChild.style.zIndex + ', position: ' + firstChild.style.position + ', display: ' + firstChild.style.display);
+          write('secondChild, z-index: ' + secondChild.style.zIndex + ', position: ' + secondChild.style.position + ', display: ' + secondChild.style.display);
+          write('container, z-index: ' + container.style.zIndex + ', position: ' + container.style.position + ', display: ' + container.style.display);
+          write('');
+        }
+
         testPermutation(permutationIteration, ordering, hasPositionedAncestor, containerIsPositioned);
         permutationIteration++;
       }
     }
   }
 }
 
 function permute(testPermutation)
 {
   var ancestor = document.getElementById('ancestor');
@@ skipping 13 matching lines @@
       containerIndices.splice(containerSubindex, 1);
       var firstChildIndex = containerIndices[0];
       var secondChildIndex = containerIndices[1];
 
       permuteWithFixedOrdering(testPermutation, siblingIndex, containerIndex, firstChildIndex, secondChildIndex, 1);
       permuteWithFixedOrdering(testPermutation, siblingIndex, containerIndex, firstChildIndex, secondChildIndex, 2);
       permuteWithFixedOrdering(testPermutation, siblingIndex, containerIndex, firstChildIndex, secondChildIndex, 3);
     }
   }
 } // function doTest