Move FileDescriptorShuffle to base/posix. This file is very posix-specific.

base/posix/file_descriptor_shuffle.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 BASE_FILE_DESCRIPTOR_SHUFFLE_H_
-#define BASE_FILE_DESCRIPTOR_SHUFFLE_H_
+#ifndef BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_
+#define BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_
 
 // This code exists to perform the shuffling of file descriptors which is
 // commonly needed when forking subprocesses. The naive approve is very simple,
 // just call dup2 to setup the desired descriptors, but wrong. It's tough to
 // handle the edge cases (like mapping 0 -> 1, 1 -> 0) correctly.
 //
 // In order to unittest this code, it's broken into the abstract action (an
 // injective multimap) and the concrete code for dealing with file descriptors.
 // Users should use the code like this:
 //   base::InjectiveMultimap file_descriptor_map;
@@ skipping 60 matching lines @@
     InjectionDelegate* delegate);
 
 // This function will not call malloc but will mutate |map|
 static inline bool ShuffleFileDescriptors(InjectiveMultimap* map) {
   FileDescriptorTableInjection delegate;
   return PerformInjectiveMultimapDestructive(map, &delegate);
 }
 
 }  // namespace base
 
-#endif  // BASE_FILE_DESCRIPTOR_SHUFFLE_H_
+#endif  // BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_