Show custom properties in the computed style pane of the inspector.

third_party/WebKit/LayoutTests/http/tests/inspector/elements-test.js

 var initialize_ElementTest = function() {
 
 InspectorTest.preloadPanel("elements");
 
 InspectorTest.inlineStyleSection = function()
 {
     return WebInspector.panels.elements.sidebarPanes.styles._sectionBlocks[0].sections[0];
 }
 
 InspectorTest.computedStyleWidget = function()
@@ skipping 264 matching lines @@
     {
         return node.parentNode && node.parentNode.getAttribute("id") === parentId && node.pseudoType() == pseudoType;
     }
 }
 
 InspectorTest.selectNodeAndWaitForStylesWithComputed = function(idValue, callback)
 {
     callback = InspectorTest.safeWrap(callback);
     InspectorTest.selectNodeAndWaitForStyles(idValue, onSidebarRendered);
 
-    function onSidebarRendered()
+    function onSidebarRendered(node)
     {
-        InspectorTest.computedStyleWidget().doUpdate().then(callback);
+        InspectorTest.computedStyleWidget().doUpdate().then(callback.bind(null, node));
     }
 }
 
 InspectorTest.firstElementsTreeOutline = function()
 {
     return WebInspector.panels.elements._treeOutlines[0];
 }
 
 InspectorTest.filterMatchedStyles = function(text)
 {
@@ skipping 672 matching lines @@
 InspectorTest.dumpAnimationTimeline = function(timeline)
 {
     for (var ui of timeline._uiAnimations) {
         InspectorTest.addResult(ui.animation().type());
         InspectorTest.addResult(ui._nameElement.innerHTML);
         InspectorTest.addResult(ui._svg.innerHTML);
     }
 }
 
 };