gpu: Reuse existing code for shared memory allocation.

base/memory/shared_memory_win.cc

Index: base/memory/shared_memory_win.cc
diff --git a/base/memory/shared_memory_win.cc b/base/memory/shared_memory_win.cc
index 7e39b45ff9740de3f3c424a2ce89642e64f3bf2c..e7a88a5f06b7b126a295e1e935da939c900624d9 100644
--- a/base/memory/shared_memory_win.cc
+++ b/base/memory/shared_memory_win.cc
@@ -379,4 +379,12 @@ 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