Support the use-case of maximal memory efficiency

[chrishtr]

In examples such as domenic/infinite-list-study-group#8,
it is critical to be able to minimize memory of a large code file by avoiding rendering-related data structures. If these turn out to lead to memory use more than 2x or so the memory for strings of text in the code file, we would need to add functionality to allow the developer to evict rendering state for offscreen content.

[fergald]

My reading of that was that they don't even want the DOM around when it's not needed (which presumably would take care of evicting rendering-related structures). That said, having the browser proactively reclaim memory from invisible parts of the screen seems reasonable but I'm not sure that we'd want it to be under control from JS, it's just something the browser could do when it feels like it (.e.g when we start getting memory pressure signals on mobile).

[chrishtr]

What they didn't want was to run out of memory. The use-case also explicitly said that it would be good to support find-in-page.

[vmpstr]

I wonder if for content-visibility: auto if we should have evict memory objects if we're far enough off-screen