Improve UI for unpacked extensions failing to load

chrome/chrome_browser_ui.gypi

 # Copyright 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.
 
 {
   'targets': [
     {
       'target_name': 'browser_ui',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 2090 matching lines @@
         'browser/ui/webui/extensions/extension_basic_info.cc',
         'browser/ui/webui/extensions/extension_basic_info.h',
         'browser/ui/webui/extensions/extension_error_handler.cc',
         'browser/ui/webui/extensions/extension_error_handler.h',
         'browser/ui/webui/extensions/extension_error_ui_util.cc',
         'browser/ui/webui/extensions/extension_error_ui_util.h',
         'browser/ui/webui/extensions/extension_icon_source.cc',
         'browser/ui/webui/extensions/extension_icon_source.h',
         'browser/ui/webui/extensions/extension_info_ui.cc',
         'browser/ui/webui/extensions/extension_info_ui.h',
+        'browser/ui/webui/extensions/extension_loader_handler.cc',
+        'browser/ui/webui/extensions/extension_loader_handler.h',
         'browser/ui/webui/extensions/extension_settings_handler.cc',
         'browser/ui/webui/extensions/extension_settings_handler.h',
         'browser/ui/webui/extensions/extensions_ui.cc',
         'browser/ui/webui/extensions/extensions_ui.h',
         'browser/ui/webui/extensions/install_extension_handler.cc',
         'browser/ui/webui/extensions/install_extension_handler.h',
         'browser/ui/webui/extensions/pack_extension_handler.cc',
         'browser/ui/webui/extensions/pack_extension_handler.h',
         'browser/ui/webui/favicon_source.cc',
         'browser/ui/webui/favicon_source.h',
@@ skipping 1023 matching lines @@
             'browser/ui/webui/local_discovery/local_discovery_ui.cc',
             'browser/ui/webui/local_discovery/local_discovery_ui.h',
             'browser/ui/webui/local_discovery/local_discovery_ui_handler.cc',
             'browser/ui/webui/local_discovery/local_discovery_ui_handler.h',
           ],
         }],
       ],
     },
   ],
 }