Improve CloudPolicyClient doc.

components/policy/core/common/cloud/cloud_policy_client.h

 // 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.
 
 #ifndef COMPONENTS_POLICY_CORE_COMMON_CLOUD_CLOUD_POLICY_CLIENT_H_
 #define COMPONENTS_POLICY_CORE_COMMON_CLOUD_CLOUD_POLICY_CLIENT_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 62 matching lines @@
 
     // Called when a request for device robot OAuth2 authorization tokens
     // returns successfully. Only occurs during enrollment. Optional
     // (default implementation is a noop).
     virtual void OnRobotAuthCodesFetched(CloudPolicyClient* client);
 
     // Indicates there's been an error in a previously-issued request.
     virtual void OnClientError(CloudPolicyClient* client) = 0;
   };
 
-  // |service| and |signing_service| are weak pointers and it's the caller's
+  // If non-empty, |machine_id| and |machine_model| are passed to the server
+  // verbatim. As these reveal machine identity, they must only be used where
+  // this is appropriate (i.e. device policy, but not user policy). |service|
+  // and |signing_service| are weak pointers and it's the caller's
   // responsibility to keep them valid for the lifetime of CloudPolicyClient.
   // |verification_key_hash| contains an identifier telling the DMServer which
   // verification key to use. The |signing_service| is used to sign sensitive
   // requests.
   CloudPolicyClient(
       const std::string& machine_id,
       const std::string& machine_model,
       const std::string& verification_key_hash,
       DeviceManagementService* service,
       scoped_refptr<net::URLRequestContextGetter> request_context,
@@ skipping 323 matching lines @@
 
   // Used to create tasks which run delayed on the UI thread.
   base::WeakPtrFactory<CloudPolicyClient> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CloudPolicyClient);
 };
 
 }  // namespace policy
 
 #endif  // COMPONENTS_POLICY_CORE_COMMON_CLOUD_CLOUD_POLICY_CLIENT_H_