[DevTools] Turn WebInspector.Panel into a web component.

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

 var initialize_ElementTest = function() {
 
 InspectorTest.preloadPanel("elements");
 
 InspectorTest.inlineStyleSection = function()
 {
     return WebInspector.panels.elements._stylesWidget._sectionBlocks[0].sections[0];
 }
 
 InspectorTest.computedStyleWidget = function()
@@ skipping 922 matching lines @@
 
 InspectorTest.addNewRuleInStyleSheet = function(styleSheetHeader, selector, callback)
 {
     InspectorTest.addSniffer(WebInspector.StylesSidebarPane.prototype, "_addBlankSection", onBlankSection.bind(null, selector, callback));
     WebInspector.panels.elements._stylesWidget._createNewRuleInStyleSheet(styleSheetHeader);
 }
 
 InspectorTest.addNewRule = function(selector, callback)
 {
     // Click "Add new rule".
-    document.querySelector(".styles-pane-toolbar").shadowRoot.querySelector(".add-toolbar-item").click();
+    WebInspector.ElementsPanel.instance()._stylesSidebarToolbar.querySelector(".styles-pane-toolbar").shadowRoot.querySelector(".add-toolbar-item").click();
     InspectorTest.addSniffer(WebInspector.StylesSidebarPane.prototype, "_addBlankSection", onBlankSection.bind(null, selector, callback));
 }
 
 function onBlankSection(selector, callback)
 {
     var section = InspectorTest.firstMatchedStyleSection();
     if (typeof selector === "string")
         section._selectorElement.textContent = selector;
     section._selectorElement.dispatchEvent(InspectorTest.createKeyEvent("Enter"));
     InspectorTest.waitForSelectorCommitted(callback.bind(null, section));
@@ skipping 23 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);
     }
 }
 
 };