Introduce HostID and de-couple Extensions from "script injection System" [browser side]

chrome/chrome_browser_extensions.gypi

 # Copyright (c) 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_chromeos_sources': [
       'browser/extensions/api/diagnostics/diagnostics_api.cc',
       'browser/extensions/api/diagnostics/diagnostics_api.h',
       'browser/extensions/api/diagnostics/diagnostics_api_chromeos.cc',
@@ skipping 643 matching lines @@
       'browser/extensions/extension_toolbar_model.cc',
       'browser/extensions/extension_toolbar_model.h',
       'browser/extensions/extension_toolbar_model_factory.cc',
       'browser/extensions/extension_toolbar_model_factory.h',
       'browser/extensions/extension_ui_util.cc',
       'browser/extensions/extension_ui_util.h',
       'browser/extensions/extension_uninstall_dialog.cc',
       'browser/extensions/extension_uninstall_dialog.h',
       'browser/extensions/extension_util.cc',
       'browser/extensions/extension_util.h',
+      'browser/extensions/extension_user_script_loader.cc',
+      'browser/extensions/extension_user_script_loader.h',
       'browser/extensions/extension_view_host.cc',
       'browser/extensions/extension_view_host.h',
       'browser/extensions/extension_view_host_factory.cc',
       'browser/extensions/extension_view_host_factory.h',
       'browser/extensions/extension_view_host_mac.h',
       'browser/extensions/extension_view_host_mac.mm',
       'browser/extensions/extension_warning_badge_service.cc',
       'browser/extensions/extension_warning_badge_service.h',
       'browser/extensions/extension_warning_badge_service_factory.cc',
       'browser/extensions/extension_warning_badge_service_factory.h',
@@ skipping 421 matching lines @@
           ],
         }, {  # use_brlapi==0
           'sources': [
             'browser/extensions/api/braille_display_private/braille_controller_stub.cc',
           ],
         }],
       ],
     },
   ],
 }