Form-associated custom elements: FormController handles ListedElement instead of HTMLFormControlElementWithState

Introduce ListedElement::ClassSupportsStateRestore(), and only
HTMLFormControlElementWithState returns true for it at this moment.

This is a preparation to support the state restore feature for
form-associated custom elements, which are not
HTMLFormControlElementWithState but are ListedElement.

This CL has no behavior changes.

Bug: 905922
Change-Id: I5931a1f9477d5122702120c8d6ddf534e14c97d8
Reviewed-on: https://chromium-review.googlesource.com/c/1433347
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626004}
6 files changed