Cancel method
void
Cancel()
Implementation
void Cancel() {
final hr = _thisPtr.ref.vtable
.elementAt(9)
.cast<Pointer<NativeFunction<HRESULT Function(Pointer)>>>()
.value
.asFunction<int Function(Pointer)>()(_thisPtr.ref.lpVtbl);
if (FAILED(hr)) throw WindowsException(hr);
}