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)
+    {
+        InspectorTest.addObject(element.__scrollRect, {layerId: "formatAsTypeName"}, "", "scrollRect: ");
+    }
+
+    InspectorTest.dumpViewScrollRects = function()
+    {
+        InspectorTest.addResult("View elements dump");
+        var root = WebInspector.panel("layers")._layers3DView._rotatingContainerElement;
+        Array.prototype.forEach.call(root.querySelectorAll('.scroll-rect'), function(element) {
+            InspectorTest.dumpViewScrollRect(element);
+        });
+    }
+
+    InspectorTest.dumpModelScrollRects = function()
+    {
+        InspectorTest.addResult("Model elements dump");
+        InspectorTest.addObject(InspectorTest._layerTreeModel._scrollRectsByLayerId, {layerId: "formatAsTypeName"}, "", "scrollRectsByLayerId: ");
+    }
 }