For c++, Generate enum classes instead of enum from mojom.

mojo/public/cpp/bindings/tests/versioning_apptest.cc

 // 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.
 
 #include "mojo/public/cpp/application/application_impl.h"
 #include "mojo/public/cpp/application/application_test_base.h"
 #include "mojo/public/cpp/system/macros.h"
 #include "mojo/public/interfaces/bindings/tests/versioning_test_client.mojom.h"
 
 namespace mojo {
@@ skipping 19 matching lines @@
  private:
   MOJO_DISALLOW_COPY_AND_ASSIGN(VersioningApplicationTest);
 };
 
 TEST_F(VersioningApplicationTest, Struct) {
   // The service side uses a newer version of Employee defintion.
   // The returned struct should be truncated.
   EmployeePtr employee(Employee::New());
   employee->employee_id = 1;
   employee->name = "Homer Simpson";
-  employee->department = DEPARTMENT_DEV;
+  employee->department = Department::DEV;
 
   database_->QueryEmployee(1, true,
                            [&employee](EmployeePtr returned_employee,
                                        Array<uint8_t> returned_finger_print) {
                              EXPECT_TRUE(employee->Equals(*returned_employee));
                              EXPECT_FALSE(returned_finger_print.is_null());
                            });
   database_.WaitForIncomingResponse();
 
   // Passing a struct of older version to the service side works.
   EmployeePtr new_employee(Employee::New());
   new_employee->employee_id = 2;
   new_employee->name = "Marge Simpson";
-  new_employee->department = DEPARTMENT_SALES;
+  new_employee->department = Department::SALES;
 
   database_->AddEmployee(new_employee.Clone(),
                          [](bool success) { EXPECT_TRUE(success); });
   database_.WaitForIncomingResponse();
 
   database_->QueryEmployee(
       2, false, [&new_employee](EmployeePtr returned_employee,
                                 Array<uint8_t> returned_finger_print) {
         EXPECT_TRUE(new_employee->Equals(*returned_employee));
         EXPECT_TRUE(returned_finger_print.is_null());
@@ skipping 47 matching lines @@
   // Calling a version 2 method (which the service side doesn't support) closes
   // the pipe.
   database_->ListEmployeeIds([](Array<uint64_t> ids) { EXPECT_TRUE(false); });
   database_.WaitForIncomingResponse();
   EXPECT_TRUE(database_.encountered_error());
 }
 
 }  // namespace versioning
 }  // namespace examples
 }  // namespace mojo