Dual of Bug 78443.
Why? FrameObserver is such a generic name that it means nothing.
We can keep the current name if that's what folks prefer. I was just worried that willDisconnectPage isn't directly related to destruction, but maybe it's close enough.
I was just wondering based on the above comment that is this change needed? Then I can propose a simple patch, otherwise we can move this issue to Invalid/Wont Fix...
Let's mark it WONTFIX for now. We might change the name in the future if we find that we want to observe more things about frames.