Put extension enable logic into a ExtensionEnableFlow.

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 791 matching lines @@
         'browser/ui/content_settings/content_setting_bubble_model.h',
         'browser/ui/content_settings/content_setting_bubble_model_delegate.h',
         'browser/ui/content_settings/content_setting_image_model.cc',
         'browser/ui/content_settings/content_setting_image_model.h',
         'browser/ui/crypto_module_password_dialog.cc',
         'browser/ui/crypto_module_password_dialog.h',
         'browser/ui/crypto_module_password_dialog_nss.cc',
         'browser/ui/crypto_module_password_dialog_openssl.cc',
         'browser/ui/extensions/application_launch.cc',
         'browser/ui/extensions/application_launch.h',
+        'browser/ui/extensions/extension_enable_flow.cc',
+        'browser/ui/extensions/extension_enable_flow.h',
+        'browser/ui/extensions/extension_enable_flow_delegate.h',
         'browser/ui/extensions/native_app_window.h',
         'browser/ui/extensions/shell_window.cc',
         'browser/ui/extensions/shell_window.h',
         'browser/ui/find_bar/find_bar.h',
         'browser/ui/find_bar/find_bar_controller.cc',
         'browser/ui/find_bar/find_bar_controller.h',
         'browser/ui/find_bar/find_bar_state.h',
         'browser/ui/find_bar/find_bar_state_factory.cc',
         'browser/ui/find_bar/find_bar_state_factory.h',
         'browser/ui/find_bar/find_notification_details.h',
@@ skipping 1979 matching lines @@
         }, { # else: enable_app_list==0
           'sources/': [
             ['exclude', '^browser/ui/views/app_list/'],
             ['exclude', '^browser/ui/app_list/'],
           ]
         }],
       ],
     },
   ],
 }