gpu: Reuse existing code for shared memory allocation.

base/memory/shared_memory_posix.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 <errno.h>
 #include <fcntl.h>
 #include <stddef.h>
 #include <sys/mman.h>
@@ skipping 361 matching lines @@
   munmap(memory_, mapped_size_);
   memory_ = NULL;
   mapped_size_ = 0;
   return true;
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return FileDescriptor(mapped_file_, false);
 }
 
+SharedMemoryHandle SharedMemory::TakeHandle() {
+  FileDescriptor handle(mapped_file_, true);
+  mapped_file_ = -1;
+  memory_ = nullptr;
+  mapped_size_ = 0;
+  return handle;
+}
+
 void SharedMemory::Close() {
   if (mapped_file_ > 0) {
     if (IGNORE_EINTR(close(mapped_file_)) < 0)
       PLOG(ERROR) << "close";
     mapped_file_ = -1;
   }
   if (readonly_mapped_file_ > 0) {
     if (IGNORE_EINTR(close(readonly_mapped_file_)) < 0)
       PLOG(ERROR) << "close";
     readonly_mapped_file_ = -1;
@@ skipping 95 matching lines @@
 
   if (close_self) {
     Unmap();
     Close();
   }
 
   return true;
 }
 
 }  // namespace base