[resize-observer] Behavior when the callback modifies depth

[smfr]

https://drafts.csswg.org/resize-observer-1/#html-event-loop

Calculate depth for node happens each time the "Gather active observations at depth" steps are run.

This implies that callback that changes the depth can trigger that observer getting called multiple times in one set of ResizeObserver notifications. For example, a call back could modify the DOM to add an element in its ancestor chain. This could lead to the steps never exiting.

One way to avoid this would be to compute the depth once per element at the start of firing ResizeObserver notifications.

[atotic]

I do not think this edge case is a problem.
For each additional loop, callback would have to add an Element to ancestor chain. This is unlikely to happen by accident. If it happens intentionally, user agent will be in an infinite loop, and also run out of memory,

[smfr]

Computing depth at the start of the algorithm would avoid this, though, and seems simple.