Persist 'this device is not managed' information

chrome/browser/policy/proto/device_management_local.proto

 // Copyright (c) 2010 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;
 
 import "device_management_backend.proto";
 
 // Wrapper around DevicePolicyResponse for caching on disk.
 message CachedDevicePolicyResponse {
   // The DevicePolicyResponse wrapped by this message.
-  required DevicePolicyResponse policy = 1;
+  optional DevicePolicyResponse policy = 1;
   // Timestamp noting when this policy was cached.
   optional uint64 timestamp = 2;
+  // Flag that is set to true if this device is not managed.
+  optional bool unmanaged = 3;
 }
 
 // Encapsulates a device ID and the associated device token.
 message DeviceCredentials {
   optional string device_id = 1;
   optional string device_token = 2;
 }