We should use UserID object to identify users instead of username.

chromeos/attestation/mock_attestation_flow.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 CHROMEOS_ATTESTATION_MOCK_ATTESTATION_FLOW_H_
 #define CHROMEOS_ATTESTATION_MOCK_ATTESTATION_FLOW_H_
 
 #include "chromeos/attestation/attestation_flow.h"
 
 #include "base/basictypes.h"
 #include "base/callback.h"
+#include "components/user_manager/user_id.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 namespace chromeos {
 namespace attestation {
 
 // A fake server proxy which just appends "_response" to every request.
 class FakeServerProxy : public ServerProxy {
  public:
   FakeServerProxy();
   ~FakeServerProxy() override;
@@ skipping 38 matching lines @@
 
   MOCK_METHOD2(MockCertificateCallback, void(bool, const std::string&));
 };
 
 class MockAttestationFlow : public AttestationFlow {
  public:
   MockAttestationFlow();
   virtual ~MockAttestationFlow();
 
   MOCK_METHOD5(GetCertificate, void(AttestationCertificateProfile,
-                                    const std::string&,
+                                    const user_manager::UserID&,
                                     const std::string&,
                                     bool,
                                     const CertificateCallback&));
 };
 
 }  // namespace attestation
 }  // namespace chromeos
 
 #endif  // CHROMEOS_ATTESTATION_MOCK_ATTESTATION_FLOW_H_