Revert of Revert of Make SharedMemoryHandle a class on Mac.

base/memory/shared_memory_handle.h

Index: base/memory/shared_memory_handle.h
diff --git a/base/memory/shared_memory_handle.h b/base/memory/shared_memory_handle.h
new file mode 100644
index 0000000000000000000000000000000000000000..7af8729976dab980c39d7ace7d0b0bef7a677637
--- /dev/null
+++ b/base/memory/shared_memory_handle.h
@@ -0,0 +1,97 @@
+// Copyright 2015 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_HANDLE_H_
+#define BASE_MEMORY_SHARED_MEMORY_HANDLE_H_
+
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <windows.h>
+#elif defined(OS_MACOSX) && !defined(OS_IOS)
+#include <sys/types.h>
+#include "base/base_export.h"
+#include "base/file_descriptor_posix.h"
+#include "base/macros.h"
+#elif defined(OS_POSIX)
+#include <sys/types.h>
+#include "base/file_descriptor_posix.h"
+#endif
+
+namespace base {
+
+class Pickle;
+
+// SharedMemoryHandle is a platform specific type which represents
+// the underlying OS handle to a shared memory segment.
+#if defined(OS_WIN)
+typedef HANDLE SharedMemoryHandle;
+#elif defined(OS_POSIX) && !(defined(OS_MACOSX) && !defined(OS_IOS))
+typedef FileDescriptor SharedMemoryHandle;
+#else
+class BASE_EXPORT SharedMemoryHandle {
+ public:
+  enum Type {
+    // Indicates that the SharedMemoryHandle is backed by a POSIX fd.
+    POSIX,
+    // Indicates that the SharedMemoryHandle is backed by the Mach primitive
+    // "memory object".
+    MACH,
+  };
+
+  // The format that should be used to transmit |Type| over the wire.
+  typedef int TypeWireFormat;
+
+  // The default constructor returns an invalid SharedMemoryHandle.
+  SharedMemoryHandle();
+
+  // Constructs a SharedMemoryHandle backed by the components of a
+  // FileDescriptor. The newly created instance has the same ownership semantics
+  // as base::FileDescriptor. This typically means that the SharedMemoryHandle
+  // takes ownership of the |fd| if |auto_close| is true. Unfortunately, it's
+  // common for existing code to make shallow copies of SharedMemoryHandle, and
+  // the one that is finally passed into a base::SharedMemory is the one that
+  // "consumes" the fd.
+  explicit SharedMemoryHandle(const base::FileDescriptor& file_descriptor);
+  SharedMemoryHandle(int fd, bool auto_close);
+
+  // Standard copy constructor. The new instance shares the underlying OS
+  // primitives.
+  SharedMemoryHandle(const SharedMemoryHandle& handle);
+
+  // Standard assignment operator. The updated instance shares the underlying
+  // OS primitives.
+  SharedMemoryHandle& operator=(const SharedMemoryHandle& handle);
+
+  // Duplicates the underlying OS resources.
+  SharedMemoryHandle Duplicate() const;
+
+  // Comparison operators.
+  bool operator==(const SharedMemoryHandle& handle) const;
+  bool operator!=(const SharedMemoryHandle& handle) const;
+
+  // Returns the type.
+  Type GetType() const;
+
+  // Whether the underlying OS primitive is valid.
+  bool IsValid() const;
+
+  // Sets the POSIX fd backing the SharedMemoryHandle. Requires that the
+  // SharedMemoryHandle be backed by a POSIX fd.
+  void SetFileHandle(int fd, bool auto_close);
+
+  // This method assumes that the SharedMemoryHandle is backed by a POSIX fd.
+  // This is eventually no longer going to be true, so please avoid adding new
+  // uses of this method.
+  const FileDescriptor GetFileDescriptor() const;
+
+ private:
+  Type type_;
+  FileDescriptor file_descriptor_;
+};
+#endif
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_SHARED_MEMORY_HANDLE_H_