Added showing slow scroll rectangles in Layers panel.

LayoutTests/http/tests/inspector/layers-test.js

 function initialize_LayerTreeTests()
 {
     // FIXME: remove once out of experimental.
     WebInspector.moduleManager.registerModule("layers");
     var extensions = WebInspector.moduleManager.extensions(WebInspector.Panel).forEach(function(extension) {
         if (extension.module().name() === "layers")
             WebInspector.inspectorView.addPanel(new WebInspector.ModuleManagerExtensionPanelDescriptor(extension));
     });
     InspectorTest._layerTreeModel = WebInspector.panel("layers")._model;
 
@@ skipping 83 matching lines @@
     InspectorTest.requestLayers = function(callback)
     {
         InspectorTest._layerTreeModel.addEventListener(WebInspector.LayerTreeModel.Events.LayerTreeChanged, onLayerTreeChanged);
         InspectorTest._layerTreeModel.enable();
         function onLayerTreeChanged()
         {
             InspectorTest._layerTreeModel.removeEventListener(WebInspector.LayerTreeModel.Events.LayerTreeChanged, onLayerTreeChanged);
             callback();
         }
     }
+
+    InspectorTest.dumpViewScrollRect = function(element)
+    {
+        var value = {
+            className: element.className,
+            title: element.title,
+            width: element.style.width,
+            height: element.style.height,
+            left: element.style.left,
+            top: element.style.top
+        };
+        if (element.__unchanged)
+            value.__unchanged = element.__unchanged;
+        InspectorTest.addObject(value, null, "", "scroll-rect: ");
+    }
+
+    InspectorTest.dumpViewScrollRects = function()
+    {
+        InspectorTest.addResult("View elements dump");
+        var root = WebInspector.panel("layers")._layers3DView._rotatingContainerElement;
+        Array.prototype.forEach.call(root.querySelectorAll('.scroll-rect'), InspectorTest.dumpViewScrollRect.bind(InspectorTest));
+    }
+
+    InspectorTest.dumpModelScrollRects = function()
+    {
+        function dumpScrollRectsForLayer(layer)
+        {
+            InspectorTest.addObject(layer._scrollRects);
+        }
+
+        InspectorTest.addResult("Model elements dump");
+        InspectorTest._layerTreeModel.forEachLayer(dumpScrollRectsForLayer.bind(this));
+    }
 }