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

services/files/util.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 SERVICES_FILES_UTIL_H_
 #define SERVICES_FILES_UTIL_H_
 
 #include "mojo/services/files/public/interfaces/types.mojom.h"
 
 namespace mojo {
 
 class String;
 
 namespace files {
 
 // Validation functions (typically used to check arguments; they return
-// |ERROR_OK| if valid, else the standard/recommended error for the validation
+// |Error::OK| if valid, else the standard/recommended error for the validation
 // error):
 
 // Checks if |path|, which must be non-null, is (looks like) a valid (relative)
-// path. (On failure, returns |ERROR_INVALID_ARGUMENT| if |path| is not UTF-8,
-// or |ERROR_PERMISSION_DENIED| if it is not relative.)
+// path. (On failure, returns |Error::INVALID_ARGUMENT| if |path| is not UTF-8,
+// or |Error::PERMISSION_DENIED| if it is not relative.)
 Error IsPathValid(const String& path);
 
 // Checks if |whence| is a valid (known) |Whence| value. (On failure, returns
-// |ERROR_UNIMPLEMENTED|.)
+// |Error::UNIMPLEMENTED|.)
 Error IsWhenceValid(Whence whence);
 
 // Checks if |offset| is a valid file offset (from some point); this is
 // implementation-dependent (typically checking if |offset| fits in an |off_t|).
-// (On failure, returns |ERROR_OUT_OF_RANGE|.)
+// (On failure, returns |Error::OUT_OF_RANGE|.)
 Error IsOffsetValid(int64_t offset);
 
 // Conversion functions:
 
 // Converts a standard errno value (|E...|) to an |Error| value.
 Error ErrnoToError(int errno_value);
 
 // Converts a |Whence| value to a standard whence value (|SEEK_...|).
 int WhenceToStandardWhence(Whence whence);
 
 // Converts a |Timespec| to a |struct timespec|. If |in| is null, |out->tv_nsec|
 // is set to |UTIME_OMIT|.
 Error TimespecToStandardTimespec(const Timespec* in, struct timespec* out);
 
 // Converts a |TimespecOrNow| to a |struct timespec|. If |in| is null,
 // |out->tv_nsec| is set to |UTIME_OMIT|; if |in->now| is set, |out->tv_nsec| is
 // set to |UTIME_NOW|.
 Error TimespecOrNowToStandardTimespec(const TimespecOrNow* in,
                                       struct timespec* out);
 
 }  // namespace files
 }  // namespace mojo
 
 #endif  // SERVICES_FILES_UTIL_H_