Update values after upgrading custom elements

[bgotink]

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[justinfagnani]

Awesome, this was next on my list :)

There's one more test that I'd like to add from user bug reports - make sure that property setters are called for custom elements inside of nested templates add after the initial render.

You can use the same custom element class in your test, but do something like this:

const t = (value: any) => html`${value}`;
render(t('A'), container);

const fragment = html`<x-test-uses-property-setters value=${'foo'}></x-test-uses-property-setters>`;
render(t(fragment), container);
// asserts

[bgotink]

Alright! I've added the extra test.

These tests only run in browsers where custom elements are natively supported, it is probably interesting to test them with the customElements shim as well. I don't have time for this atm, but I'd be willing to look into that later this week.

[justinfagnani]

Thanks a lot!