Revert of Remove IPC::BrokerableAttachment.

ipc/ipc_platform_file_attachment_posix.cc

 // Copyright (c) 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 "ipc/ipc_platform_file_attachment_posix.h"
 
 #include <utility>
 
 namespace IPC {
 namespace internal {
 
 PlatformFileAttachment::PlatformFileAttachment(base::PlatformFile file)
     : file_(file) {
 }
 
 PlatformFileAttachment::PlatformFileAttachment(base::ScopedFD file)
     : file_(file.get()), owning_(std::move(file)) {}
 
 PlatformFileAttachment::~PlatformFileAttachment() {
 }
 
 MessageAttachment::Type PlatformFileAttachment::GetType() const {
-  return Type::PLATFORM_FILE;
+  return TYPE_PLATFORM_FILE;
 }
 
 base::PlatformFile PlatformFileAttachment::TakePlatformFile() {
   ignore_result(owning_.release());
   return file_;
 }
 
 base::PlatformFile GetPlatformFile(
     scoped_refptr<MessageAttachment> attachment) {
-  DCHECK_EQ(attachment->GetType(), MessageAttachment::Type::PLATFORM_FILE);
+  DCHECK_EQ(attachment->GetType(), MessageAttachment::TYPE_PLATFORM_FILE);
   return static_cast<PlatformFileAttachment*>(attachment.get())->file();
 }
 
 }  // namespace internal
 }  // namespace IPC