reland 31875. Revert was:...

ipc/ipc_platform_file.h

+// Copyright (c) 2009 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 IPC_IPC_PLATFORM_FILE_H_
+#define IPC_IPC_PLATFORM_FILE_H_
+
+#include "base/basictypes.h"
+
+#include "base/platform_file.h"
+
+#if defined(OS_POSIX)
+#include "base/file_descriptor_posix.h"
+#endif
+
+namespace IPC {
+
+#if defined(OS_WIN)
+typedef base::PlatformFile PlatformFileForTransit;
+#elif defined(OS_POSIX)
+typedef base::FileDescriptor PlatformFileForTransit;
+#endif
+
+inline base::PlatformFile PlatformFileForTransitToPlatformFile(
+    const PlatformFileForTransit& transit) {
+#if defined(OS_WIN)
+  return transit;
+#elif defined(OS_POSIX)
+  return transit.fd;
+#endif
+}
+
+}  // namespace IPC
+
+#endif  // IPC_IPC_PLATFORM_FILE_H_