Enable fetching of admin policies for login screen apps

components/policy/proto/device_management_backend.proto

 // 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package enterprise_management;
 
@@ skipping 166 matching lines @@
 message PolicyFetchRequest {
   // This is the policy type, which maps to D3 policy type internally.
   // By convention, we use "/" as separator to create policy namespace.
   // The policy type names are case insensitive.
   //
   // Possible values for Chrome OS are:
   //   google/chromeos/device => ChromeDeviceSettingsProto
   //   google/chromeos/user => ChromeSettingsProto
   //   google/chromeos/publicaccount => ChromeSettingsProto
   //   google/chrome/extension => ExternalPolicyData
+  //   google/chromeos/signinextension => ExternalPolicyData
   //   google/android/user => ChromeSettingsProto
   //   google/ios/user => ChromeSettingsProto
   optional string policy_type = 1;
 
   // This is the last policy timestamp that client received from server.
   optional int64 timestamp = 2;
 
   // Tell server what kind of security signature is required.
   enum SignatureType {
     NONE = 0;
@@ skipping 1209 matching lines @@
   // Response to update device attribute.
   optional DeviceAttributeUpdateResponse device_attribute_update_response = 16;
 
   // Response to GCM id update request.
   optional GcmIdUpdateResponse gcm_id_update_response = 17;
 
   // Response to check Android management request.
   optional CheckAndroidManagementResponse
       check_android_management_response = 18;
 }