Allow performance tests to test full rendering performance

PerformanceTests/Layout/resources/floats.js

 (function() {
     function createElement(tag, parent, className, id) {
         var el = document.createElement(tag);
         el.className = className;
         if (id)
             el.id = id;
         parent.appendChild(el);
         return el;
     }
 
@@ skipping 31 matching lines @@
         runs = runs || 10;
         return function() {
             for (var c = 0; c < rows; ++c) {
                 container = containers[c];
                 container.style.display = "block";
                 for (var i = 0; i < runs; ++i) {
                     var x = Math.floor(Math.random() * width);
                     var y = Math.floor(Math.random() * height);
                     var el = document.getElementById("float" + x + "_" + y);
                     el.className = toggle(el.className, "float", "float big");
-                    // Force a layout.
-                    container.clientHeight;
+                    PerfTestRunner.forceLayoutOrFullFrame();
                 }
                 resetTest();
                 container.style.display = "none";
             }
         }
     }
     
     window.createFloatsLayoutTestFunction = createTestFunction;
 })();