DevTools: migrate sidebar pane's titleElement to use Toolbar.

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 338 matching lines @@
             printStyleSection(section, omitLonghands, includeSelectorGroupMarks);
         }
     }
 }
 
 function printStyleSection(section, omitLonghands, includeSelectorGroupMarks)
 {
     if (!section)
         return;
     InspectorTest.addResult("[expanded] " + (section.element.classList.contains("no-affect") ? "[no-affect] " : ""));
-    var chainEntries = section.titleElement.querySelectorAll(".media-list .media");
+    var chainEntries = section._titleElement.querySelectorAll(".media-list .media");
     chainEntries = Array.prototype.slice.call(chainEntries);
-    if (section.titleElement.children[1])
-        chainEntries.push(section.titleElement.children[1]);
+    if (section._titleElement.children[1])
+        chainEntries.push(section._titleElement.children[1]);
 
     for (var j = 0; j < chainEntries.length; ++j) {
         var chainEntry = chainEntries[j];
         var entryLine = includeSelectorGroupMarks ? buildMarkedSelectors(chainEntry.children[1]) : chainEntry.children[1].textContent;
         if (chainEntry.children[2])
             entryLine += " " + chainEntry.children[2].textContent;
         entryLine += " (" + extractText(chainEntry.children[0]) + ")";
         InspectorTest.addResult(entryLine);
     }
     InspectorTest.dumpStyleTreeOutline(section.propertiesTreeOutline, omitLonghands ? 1 : 2);
@@ skipping 620 matching lines @@
         for (nodeRow of nodeUI._rows) {
             for (var ui of nodeRow.animations) {
                 InspectorTest.addResult(ui._nameElement.outerHTML);
                 InspectorTest.addResult(ui._svg.outerHTML);
             }
         }
     }
 }
 
 };