Have LazyBackgroundTaskQueue notify consumers when the transient page fails to

chrome/browser/ui/webui/extensions/extension_settings_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/extensions/extension_settings_handler.h"
 
 #include "base/auto_reset.h"
 #include "base/base64.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 800 matching lines @@
 ExtensionUninstallDialog*
 ExtensionSettingsHandler::GetExtensionUninstallDialog() {
   if (!extension_uninstall_dialog_.get()) {
     extension_uninstall_dialog_.reset(
         ExtensionUninstallDialog::Create(Profile::FromWebUI(web_ui()), this));
   }
   return extension_uninstall_dialog_.get();
 }
 
 void ExtensionSettingsHandler::InspectExtensionHost(ExtensionHost* host) {
-  DevToolsWindow::OpenDevToolsWindow(host->render_view_host());
+  if (host)
+    DevToolsWindow::OpenDevToolsWindow(host->render_view_host());
 }