[DevTools] Resources panel SideBarTreeElement should show expand/collapse option only if it has chi…

LayoutTests/http/tests/inspector/indexeddb/resources-panel.html

Index: LayoutTests/http/tests/inspector/indexeddb/resources-panel.html
diff --git a/LayoutTests/http/tests/inspector/indexeddb/resources-panel.html b/LayoutTests/http/tests/inspector/indexeddb/resources-panel.html
index a567151eb7ce1bbc3cb7e859b76a7c0e0bd23afc..7300632a6726861d5a7704a1ba0a011faf52db78 100644
--- a/LayoutTests/http/tests/inspector/indexeddb/resources-panel.html
+++ b/LayoutTests/http/tests/inspector/indexeddb/resources-panel.html
@@ -43,7 +43,8 @@ function test()
         }
     }
 
-    WebInspector.showPanel("resources");
+    // Load panel to install listeners.
+    WebInspector.panel("resources");
 
     InspectorTest.addSniffer(WebInspector.IndexedDBTreeElement.prototype, "_indexedDBAdded", indexedDBAdded, true);
     function indexedDBAdded()
@@ -63,6 +64,8 @@ function test()
         InspectorTest.addResult("Database loaded.");
     }
 
+    WebInspector.showPanel("resources");
+
     InspectorTest.addResult("Expanded IndexedDB tree element.");
     WebInspector.panels.resources.indexedDBListTreeElement.expand();