gpu: Reuse existing code for shared memory allocation.

base/memory/shared_memory_mac.cc

 // 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.
 
 #include "base/memory/shared_memory.h"
 
 #include <mach/mach_vm.h>
 
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
@@ skipping 159 matching lines @@
                      mapped_size_);
   memory_ = NULL;
   mapped_size_ = 0;
   return true;
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return shm_;
 }
 
+SharedMemoryHandle SharedMemory::TakeHandle() {
+  NOTREACHED();

[sadrul, 2016/11/11 02:00:30]

Can I do return std::move(shm_);?

[Nico, 2016/11/14 18:53:51]

erikchen wrote this. Erik, can you answer?

[erikchen, 2016/11/14 19:37:53]

SharedMemoryHandle doesn't have ownership semantics, so std::move doesn't make
much sense.

Duplicate()/Close() increments and decrements a mach port reference count so you
could theoretically skip it, but Duplicate() also modifies
ownership_passes_to_ipc_. To be more similar to the other platforms, I recommend
just keeping the Duplicate()/Close().

+  return SharedMemoryHandle();
+}
+
 void SharedMemory::Close() {
   shm_.Close();
   shm_ = SharedMemoryHandle();
 }
 
 bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                         SharedMemoryHandle* new_handle,
                                         bool close_self,
                                         ShareMode share_mode) {
   DCHECK(shm_.IsValid());
@@ skipping 14 matching lines @@
 
   if (close_self) {
     Unmap();
     Close();
   }
 
   return success;
 }
 
 }  // namespace base