cancel method
void
cancel()
Implementation
void cancel() {
final hr = ptr.ref.vtable
.elementAt(9)
.cast<Pointer<NativeFunction<HRESULT Function(VTablePointer lpVtbl)>>>()
.value
.asFunction<int Function(VTablePointer lpVtbl)>()(ptr.ref.lpVtbl);
if (FAILED(hr)) throwWindowsException(hr);
}