We prevented synchronous hit testing on clipped iframes if any of its ancestor clip does not preserve 2d axis alignment. However, this also makes iframes in the following situation hit test asynchronously:

<!--- No other clips at all -->
<iframe style="transform: rotateZ(45deg)" src=.../>
<!--- No other clips at all -->

The reason is that the iframe is considered clipped. We should be able to compute the correct region in this common situation.