chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/login/enrollment/enterprise_enrollment_helper_mock.h

 // Copyright 2015 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 CHROME_BROWSER_CHROMEOS_LOGIN_ENROLLMENT_ENTERPRISE_ENROLLMENT_HELPER_MOCK_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_ENROLLMENT_ENTERPRISE_ENROLLMENT_HELPER_MOCK_H_
 
 #include <string>
 
 #include "chrome/browser/chromeos/login/enrollment/enterprise_enrollment_helper.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace chromeos {
 
-class EnterpriseEnrollmentHelperImpl;
-
 // Mocks out EnterpriseEnrollmentHelper.
 class EnterpriseEnrollmentHelperMock : public EnterpriseEnrollmentHelper {
  public:
   explicit EnterpriseEnrollmentHelperMock(
       EnrollmentStatusConsumer* status_consumer);
   ~EnterpriseEnrollmentHelperMock() override;
 
   EnrollmentStatusConsumer* status_consumer();
 
   MOCK_METHOD2(EnrollUsingAuthCode,
                void(const std::string& auth_code, bool fetch_additional_token));
   MOCK_METHOD1(EnrollUsingToken, void(const std::string& token));
   MOCK_METHOD0(EnrollUsingAttestation, void());
   MOCK_METHOD0(GetDeviceAttributeUpdatePermission, void());
   MOCK_METHOD2(UpdateDeviceAttributes,
                void(const std::string& asset_id, const std::string& location));
   MOCK_METHOD1(ClearAuth, void(const base::Closure& callback));
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_ENROLLMENT_ENTERPRISE_ENROLLMENT_HELPER_MOCK_H_