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

mojo/services/files/public/c/lib/directory_wrapper.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 "files/public/c/lib/directory_wrapper.h"
 
 #include <errno.h>
 
 #include "files/public/c/lib/errno_impl.h"
 #include "files/public/c/lib/file_fd_impl.h"
@@ skipping 53 matching lines @@
     mojo_open_flags |= mojo::files::kOpenFlagTruncate;
   if ((oflag & MOJIO_O_APPEND))
     mojo_open_flags |= mojo::files::kOpenFlagAppend;
   // TODO(vtl): What should we do we open flags we don't support? And invalid
   // flags?
 
   // TODO(vtl): We currently totally ignore |mode|; maybe we should do something
   // with it?
 
   mojo::files::FilePtr file;
-  mojo::files::Error error = mojo::files::ERROR_INTERNAL;
+  mojo::files::Error error = mojo::files::Error::INTERNAL;
   directory_->OpenFile(path, mojo::GetProxy(&file), mojo_open_flags,
                        Capture(&error));
   if (!directory_.WaitForIncomingResponse()) {
     // This may be somewhat surprising. The implication is that the CWD is
     // stale, which may be a little strange.
     errno_setter.Set(ESTALE);
     return nullptr;
   }
   if (!errno_setter.Set(ErrorToErrno(error)))
     return nullptr;
   // C++11, why don't you have make_unique?
   return std::unique_ptr<FDImpl>(new FileFDImpl(errno_impl_, file.Pass()));
 }
 
 bool DirectoryWrapper::Chdir(const char* path) {
   ErrnoImpl::Setter errno_setter(errno_impl_);
 
   if (!path)
     return errno_setter.Set(EFAULT);
 
   mojo::files::DirectoryPtr new_directory;
-  mojo::files::Error error = mojo::files::ERROR_INTERNAL;
+  mojo::files::Error error = mojo::files::Error::INTERNAL;
   directory_->OpenDirectory(
       path, mojo::GetProxy(&new_directory),
       mojo::files::kOpenFlagRead | mojo::files::kOpenFlagWrite,
       Capture(&error));
   if (!directory_.WaitForIncomingResponse()) {
     // This may be somewhat surprising. The implication is that the CWD is
     // stale, which may be a little strange.
     return errno_setter.Set(ESTALE);
   }
   if (!errno_setter.Set(ErrorToErrno(error)))
     return false;
   directory_ = new_directory.Pass();
   return true;
 }
 
 }  // namespace mojio