gpu: Reuse existing code for shared memory allocation.

base/memory/shared_memory_win.cc

 // Copyright (c) 2011 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 <aclapi.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 361 matching lines @@
 
 
 void SharedMemory::Close() {
   mapped_file_.Close();
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return SharedMemoryHandle(mapped_file_.Get(), base::GetCurrentProcId());
 }
 
+SharedMemoryHandle SharedMemory::TakeHandle() {
+  SharedMemoryHandle handle(mapped_file_.Take(), base::GetCurrentProcId());
+  handle.SetOwnershipPassesToIPC(true);
+  memory_ = nullptr;
+  mapped_size_ = 0;
+  return handle;
+}
+
 }  // namespace base