Add POSIX shared memory support for Mac

base/memory/shared_memory_helper.h

Index: base/memory/shared_memory_helper.h
diff --git a/base/memory/shared_memory_helper.h b/base/memory/shared_memory_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..b515828c08c4952bdfba476b65ebca878f1fe487
--- /dev/null
+++ b/base/memory/shared_memory_helper.h
@@ -0,0 +1,33 @@
+// Copyright 2016 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_HELPER_H_
+#define BASE_MEMORY_SHARED_MEMORY_HELPER_H_
+
+#include "base/memory/shared_memory.h"
+
+#include <fcntl.h>
+
+namespace base {
+
+#if !defined(OS_ANDROID)
+// Makes a temporary file, fdopens it, and then unlinks it. |fp| is populated
+// with the fdopened FILE. |readonly_fd| is populated with the opened fd if
+// options.share_read_only is true. |path| is populated with the location of
+// the file before it was unlinked.
+// Returns false if there's an unhandled failure.
+bool CreateAnonymousSharedMemory(const SharedMemoryCreateOptions& options,
+                                 ScopedFILE* fp,
+                                 ScopedFD* readonly_fd,
+                                 FilePath* path);
+
+// Takes the outputs of CreateAnonymousSharedMemory and maps them properly to
+// |mapped_file| or |readonly_mapped_file|, depending on which one is populated.
+bool PrepareMapFile(ScopedFILE fp, ScopedFD readonly_fd, int* mapped_file,
+                    int* readonly_mapped_file);
+#endif
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_SHARED_MEMORY_HELPER_H_