IPC::Message Refactoring: Move POSIX specific bits to PlatformFileAttachment

ipc/ipc_platform_file_attachment.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.h"
-
-namespace IPC {
-namespace internal {
-
-PlatformFileAttachment::PlatformFileAttachment(base::PlatformFile file)
-    : file_(file) {
-}
-
-PlatformFileAttachment::~PlatformFileAttachment() {
-}
-
-MessageAttachment::Type PlatformFileAttachment::GetType() const {
-  return TYPE_PLATFORM_FILE;
-}
-
-base::PlatformFile GetPlatformFile(
-    scoped_refptr<MessageAttachment> attachment) {
-  DCHECK_EQ(attachment->GetType(), MessageAttachment::TYPE_PLATFORM_FILE);
-  return static_cast<PlatformFileAttachment*>(attachment.get())->file();
-}
-
-}  // namespace internal
-}  // namespace IPC