The only class that implements didNotifySubtreeInsertions is Node and HTMLFrameElementBase. We shouldn't even have this function on Node. Simply check whether a given node is a HTMLFrameElementBase or not when we're constructing m_postInsertionNotificationTargets.
This change was inspired by https://chromium.googlesource.com/chromium/blink/+/390c8633df7ead11d6440788b5b269126f171c37
<rdar://problem/15228077>
Nm... this code is already optimized by having insertedInto return InsertionNotificationRequest. I guess we're not paying any extra cost here.
Created attachment 214229 [details] Work in progress
rniwa@webkit.org - Is something needed now or we can mark this as "RESOLVED WONTFIX"? Thanks!
This is won't fix at this point.