mac: Add auto-close and share-read-only functionality to SharedMemory.

base/memory/shared_memory_handle.h

 // 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)
@@ skipping 138 matching lines @@
 
   // The SharedMemoryHandle must be valid.
   // Returns whether the SharedMemoryHandle was successfully mapped into memory.
   // On success, |memory| is an output variable that contains the start of the
   // mapped memory.
   bool MapAt(off_t offset, size_t bytes, void** memory, bool read_only);
 
   // Closes the underlying OS primitive.
   void Close() const;
 
+  void SetOwnershipPassesToIPC(bool ownership_passes);
+  bool OwnershipPassesToIPC() const;
+
  private:
   // Shared code between copy constructor and operator=.
   void CopyRelevantData(const SharedMemoryHandle& handle);
 
   Type type_;
 
   // Each instance of a SharedMemoryHandle is backed either by a POSIX fd or a
   // mach port. |type_| determines the backing member.
   union {
     FileDescriptor file_descriptor_;
 
     struct {
       mach_port_t memory_object_;
 
       // The size of the shared memory region when |type_| is MACH. Only
       // relevant if |memory_object_| is not |MACH_PORT_NULL|.
       mach_vm_size_t size_;
 
       // The pid of the process in which |memory_object_| is usable. Only
       // relevant if |memory_object_| is not |MACH_PORT_NULL|.
       base::ProcessId pid_;
+
+      // Whether passing this object as a parameter to an IPC message passes
+      // ownership of |memory_object_| to the IPC stack. This is meant to mimic
+      // the behavior of the |auto_close| parameter of FileDescriptor.
+      // Defaults to |false|.
+      bool ownership_passes_to_ipc_;
     };
   };
 };
 #endif
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_HANDLE_H_