If there is a device id use that instead of a new one for re-enrolling.

chrome/browser/policy/cloud_policy_controller.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/policy/cloud_policy_controller.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 228 matching lines @@
       // Will retry last operation but gracefully backing off.
       SetState(STATE_POLICY_ERROR);
       return;
   }
 
   NOTREACHED();
   SetState(STATE_POLICY_ERROR);
 }
 
 void CloudPolicyController::OnDeviceTokenChanged() {
-  if (data_store_->device_token().empty())
+  if (data_store_->device_token().empty()) {
+    // Additionally clear the generated device id to ensure we don't reuse old
+    // ids which could be potentially used for user tracking.
+    data_store_->set_device_id(std::string());
     SetState(STATE_TOKEN_UNAVAILABLE);
-  else
+  } else {
     SetState(STATE_TOKEN_VALID);
+  }
 }
 
 void CloudPolicyController::OnCredentialsChanged() {
   // This notification is only interesting if we don't have a device token.
   // If we already have a device token, that must be matching the current
   // user, because (1) we always recreate the policy subsystem after user
   // login (2) tokens are cached per user.
   if (data_store_->device_token().empty()) {
     notifier_->Inform(CloudPolicySubsystem::UNENROLLED,
                       CloudPolicySubsystem::NO_DETAILS,
@@ skipping 47 matching lines @@
 
 bool CloudPolicyController::ReadyToFetchToken() {
   return data_store_->token_cache_loaded() &&
          !data_store_->user_name().empty() &&
          data_store_->has_auth_token();
 }
 
 void CloudPolicyController::FetchToken() {
   if (ReadyToFetchToken()) {
     if (CanBeInManagedDomain(data_store_->user_name())) {
-      // Generate a new random device id. (It'll only be kept if registration
-      // succeeds.)
-      data_store_->set_device_id(base::GenerateGUID());
+      // Either use an already prepopulated id or generate a new random device
+      // id. (It'll only be kept if registration succeeds.)
+      if (data_store_->device_id().empty())
+        data_store_->set_device_id(base::GenerateGUID());
       token_fetcher_->FetchToken();
     } else {
       SetState(STATE_TOKEN_UNMANAGED);
     }
   } else {
     VLOG(1) << "Not ready to fetch DMToken yet, will try again later.";
   }
 }
 
 void CloudPolicyController::SendPolicyRequest() {
@@ skipping 152 matching lines @@
 
 base::Time CloudPolicyController::GetLastRefreshTime(const base::Time& now) {
   base::Time last_refresh(cache_->last_policy_refresh_time());
   if (last_refresh.is_null())
     last_refresh = now;
 
   return last_refresh;
 }
 
 }  // namespace policy