Deprecate the External Extension Install via Preferences file (Windows only).

chrome/browser/extensions/external_provider_impl.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/extensions/external_provider_impl.h"
 
 #include <set>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 443 matching lines @@
               service,
               app_pack_updater->CreateExternalLoader(),
               profile,
               Manifest::EXTERNAL_PREF,
               Manifest::INVALID_LOCATION,
               Extension::NO_FLAGS)));
   }
 #endif
 
   if (!profile->IsManaged() && !is_chromeos_demo_session) {
+#if !defined(OS_WIN)
     provider_list->push_back(
         linked_ptr<ExternalProviderInterface>(
             new ExternalProviderImpl(
                 service,
                 new ExternalPrefLoader(chrome::DIR_EXTERNAL_EXTENSIONS,
                                        check_admin_permissions_on_mac),
                 profile,
                 Manifest::EXTERNAL_PREF,
                 Manifest::EXTERNAL_PREF_DOWNLOAD,
                 bundled_extension_creation_flags)));
+#endif
 
 #if defined(OS_CHROMEOS) || defined (OS_MACOSX)
     // Define a per-user source of external extensions.
     // On Chrome OS, this serves as a source for OEM customization.
     provider_list->push_back(
         linked_ptr<ExternalProviderInterface>(
             new ExternalProviderImpl(
                 service,
                 new ExternalPrefLoader(chrome::DIR_USER_EXTERNAL_EXTENSIONS,
                                        ExternalPrefLoader::NONE),
@@ skipping 37 matching lines @@
             service,
             new ExternalComponentLoader(profile),
             profile,
             Manifest::INVALID_LOCATION,
             Manifest::EXTERNAL_COMPONENT,
             Extension::FROM_WEBSTORE | Extension::WAS_INSTALLED_BY_DEFAULT)));
   }
 }
 
 }  // namespace extensions