cleanup: Use ExtensionRegistryObserver in Uber

chrome/chrome_tests.gypi

 # Copyright 2013 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.
 {
   'variables': {
     'chrome_browser_extensions_test_support_sources': [
       # A list of sources which is shared between different browser tests.
       'browser/apps/app_browsertest_util.cc',
       'browser/apps/app_browsertest_util.h',
       'browser/extensions/browsertest_util.cc',
@@ skipping 510 matching lines @@
       'browser/ui/webui/ntp/new_tab_page_sync_handler_browsertest.cc',
       'browser/ui/webui/ntp/new_tab_ui_browsertest.cc',
       'browser/ui/webui/options/clear_browser_data_browsertest.cc',
       'browser/ui/webui/options/options_browsertest.cc',
       'browser/ui/webui/options/options_ui_browsertest.cc',
       'browser/ui/webui/options/options_ui_browsertest.h',
       'browser/ui/webui/password_manager_internals/password_manager_internals_ui_browsertest.cc',
       'browser/ui/webui/print_preview/print_preview_ui_browsertest.cc',
       'browser/ui/webui/signin/inline_login_ui_browsertest.cc',
       'browser/ui/webui/signin/user_manager_ui_browsertest.cc',
+      'browser/ui/webui/uber/uber_ui_browsertest.cc',
       'browser/ui/webui/web_ui_test_handler.cc',
       'browser/ui/webui/web_ui_test_handler.h',
       'browser/ui/webui/webui_webview_browsertest.cc',
       'browser/ui/zoom/zoom_controller_browsertest.cc',
       'browser/unload_browsertest.cc',
       'common/mac/app_mode_chrome_locator_browsertest.mm',
       'common/mac/mock_launchd.cc',
       'common/mac/mock_launchd.h',
       'common/time_format_browsertest.cc',
       'renderer/autofill/autofill_renderer_browsertest.cc',
@@ skipping 2635 matching lines @@
             ['enable_webrtc==1', {
               'dependencies': [
                 '../third_party/libjingle/libjingle.gyp:libjingle_webrtc'
               ]
             }],
           ],
         }]
     }],
   ],  # 'conditions'
 }