staples.com removes the initiating field.
agoda.com credit card.
May have similar roots.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1421e630a25a367b9c70dd190bc994ab91dfbd70

commit 1421e630a25a367b9c70dd190bc994ab91dfbd70
Author: Parastoo Geranmayeh <parastoog@google.com>
Date: Wed Jul 25 15:57:03 2018

[Autofill] Dynamic Form: update the triggering element.

If the triggering element is no longer valid, update it, before
checking if a triggering a refill is necessary. While updating the
old element, check for nameless forms and unowned elements as well.
Also, if the triggering element is not filled, triggering a refill
is necessary.
Tests added.

Fixes (Desktop): etsy, staple and ysl.

Bug:  863575 
Change-Id: Id9a775a31a345c5c722687df5958c55b662ebbfd
Reviewed-on: https://chromium-review.googlesource.com/1145486
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Commit-Queue: Parastoo Geranmayeh <parastoog@google.com>
Cr-Commit-Position: refs/heads/master@{#577911}
[modify] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/chrome/browser/autofill/autofill_interactive_uitest.cc
[add] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/chrome/test/data/autofill/dynamic_form_element_invalid.html
[add] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/chrome/test/data/autofill/dynamic_form_element_invalid_noname_form.html
[add] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/chrome/test/data/autofill/dynamic_form_element_invalid_unowned.html
[modify] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/components/autofill/content/renderer/autofill_agent.cc
[modify] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/components/autofill/content/renderer/autofill_agent.h
[modify] https://crrev.com/1421e630a25a367b9c70dd190bc994ab91dfbd70/components/autofill/core/browser/autofill_manager.cc