Consider merging https://chromium.googlesource.com/chromium/blink/+/87cc87c21bcf50b1622fc21533c76d1553a703ac insertAdjacentElement, insertAdjacentText and insertAdjacentHTML should all lazyAttach just like appendChild() would have. I also removed some redundant ASSERT_WITH_SECURITY_IMPLICATIONS that aren't needed since we use toElement() right below them which contains the same assert.
lazyAttach is not something in Webkit. So marking this as "RESOLVED WONTFIX".