compositing/iframes/connect-compositing-iframe.html
compositing/update-paint-phases.html

I discovered this because I had a bug in https://codereview.chromium.org/2380683006,
causing window.internals.layerTreAsText to always report invalidations. This caused
it to surface existing under-invalidations to me.

In addition to fixing the above under-invalidations, we should have all layout tests
always print out found under-invalidations.