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

services/files/files_impl.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 "services/files/files_impl.h"
 
 #include <fcntl.h>
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ skipping 61 matching lines @@
     DCHECK(temp_dir);
   } else if (file_system.get() == std::string("debug")) {
 #ifdef NDEBUG
     LOG(WARNING) << "~/MojoDebug only available in Debug builds";
 #else
     // TODO(vtl): ScopedGeneric (hence ScopedFD) doesn't have an operator=!
     dir_fd.reset(OpenMojoDebugDirectory().release());
 #endif
     if (!dir_fd.is_valid()) {
       LOG(ERROR) << "~/MojoDebug unavailable";
-      callback.Run(ERROR_UNAVAILABLE);
+      callback.Run(Error::UNAVAILABLE);
       return;
     }
   } else {
     LOG(ERROR) << "Unknown file system: " << file_system.get();
-    callback.Run(ERROR_UNIMPLEMENTED);
+    callback.Run(Error::UNIMPLEMENTED);
     return;
   }
 
   new DirectoryImpl(directory.Pass(), dir_fd.Pass(), temp_dir.Pass());
-  callback.Run(ERROR_OK);
+  callback.Run(Error::OK);
 }
 
 }  // namespace files
 }  // namespace mojo