Revert of base: Make shared memory backed by Mach primitives by default.

base/memory/shared_memory.h

 // Copyright (c) 2012 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_MEMORY_SHARED_MEMORY_H_
 #define BASE_MEMORY_SHARED_MEMORY_H_
 
 #include "build/build_config.h"
 
 #include <string>
@@ skipping 122 matching lines @@
   bool CreateAndMapAnonymous(size_t size);
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
   // These two methods are analogs of CreateAndMapAnonymous and CreateAnonymous
   // that force the underlying OS primitive to be a POSIX fd. Do not add new
   // uses of these methods unless absolutely necessary, since constructing a
   // fd-backed SharedMemory object frequently takes 100ms+.
   // http://crbug.com/466437.
   bool CreateAndMapAnonymousPosix(size_t size);
   bool CreateAnonymousPosix(size_t size);
+
+  // This method is an analog of CreateAndMapAnonymous that forces the
+  // underlying OS primitive to be a Mach memory object.
+  bool CreateAndMapAnonymousMach(size_t size);
 #endif  // defined(OS_MACOSX) && !defined(OS_IOS)
 
   // Creates an anonymous shared memory segment of size size.
   // Returns true on success and false on failure.
   bool CreateAnonymous(size_t size) {
     SharedMemoryCreateOptions options;
     options.size = size;
     return Create(options);
   }
 
@@ skipping 147 matching lines @@
   size_t             mapped_size_;
   void*              memory_;
   bool               read_only_;
   size_t             requested_size_;
 
   DISALLOW_COPY_AND_ASSIGN(SharedMemory);
 };
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_H_