Make PlatformFileForTransit a class on Windows.

ipc/ipc_platform_file.h

 // Copyright (c) 2011 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/files/file.h"
 #include "base/process/process.h"
 #include "build/build_config.h"
 #include "ipc/ipc_export.h"
 
 #if defined(OS_POSIX)
 #include "base/file_descriptor_posix.h"
 #endif
 
+#if defined(OS_WIN)
+#include "base/memory/shared_memory_handle.h"
+#endif
+
 namespace IPC {
 
 #if defined(OS_WIN)
-typedef base::PlatformFile PlatformFileForTransit;
+// The semantics for IPC transfer of a SharedMemoryHandle are exactly the same
+// as for a PlatformFileForTransit. The object wraps a HANDLE, and has some
+// metadata that indicates the process to which the HANDLE belongs.
+using PlatformFileForTransit = base::SharedMemoryHandle;
 #elif defined(OS_POSIX)
 typedef base::FileDescriptor PlatformFileForTransit;
 #endif
 
 inline PlatformFileForTransit InvalidPlatformFileForTransit() {
 #if defined(OS_WIN)
-  return INVALID_HANDLE_VALUE;
+  return PlatformFileForTransit();
 #elif defined(OS_POSIX)
   return base::FileDescriptor();
 #endif
 }
 
 inline base::PlatformFile PlatformFileForTransitToPlatformFile(
     const PlatformFileForTransit& transit) {
 #if defined(OS_WIN)
-  return transit;
+  return transit.GetHandle();
 #elif defined(OS_POSIX)
   return transit.fd;
 #endif
 }
 
 inline base::File PlatformFileForTransitToFile(
     const PlatformFileForTransit& transit) {
 #if defined(OS_WIN)
-  return base::File(transit);
+  return base::File(transit.GetHandle());
 #elif defined(OS_POSIX)
   return base::File(transit.fd);
 #endif
 }
 
 // Returns a file handle equivalent to |file| that can be used in |process|.
 IPC_EXPORT PlatformFileForTransit GetFileHandleForProcess(
     base::PlatformFile file,
     base::ProcessHandle process,
     bool close_source_handle);
 
 // Returns a file handle equivalent to |file| that can be used in |process|.
 // Note that this function takes ownership of |file|.
 IPC_EXPORT PlatformFileForTransit TakeFileHandleForProcess(
     base::File file,
     base::ProcessHandle process);
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_PLATFORM_FILE_H_