Possible fixes:
- install the input handler when receiving the first input event
- only remove attribute if the event is trusted (user input).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/30a800ab092d8a2c24aee9e9ed73e55352ad1970

commit 30a800ab092d8a2c24aee9e9ed73e55352ad1970
Author: Elodie Banel <lod@google.com>
Date: Fri Dec 22 14:52:56 2017

Only reset autofill attributes if change is user-initiated.

The isTrusted attribute indicates that the change came from the user.
Use it to make sure we don't unset the autofill attributes when
sending our own "input" event.

Bug:  796224 
Change-Id: I7502274ba3dbe7d323382af3d884ded005f79bf0
Reviewed-on: https://chromium-review.googlesource.com/840005
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Elodie Banel <lod@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525993}
[modify] https://crrev.com/30a800ab092d8a2c24aee9e9ed73e55352ad1970/components/autofill/ios/browser/resources/autofill_controller.js

lod is OOO this week, I will continue working on this bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f1a95e3cea56b7025baf0981fc831707b361f6af

commit f1a95e3cea56b7025baf0981fc831707b361f6af
Author: Olivier Robin <olivierrobin@chromium.org>
Date: Fri Jan 05 10:15:29 2018

Autofill iOS - Fix reset forms

1. Fix reseting select by using "options" instead of option.
2. If form is "", reset the unowned fields.

Bug:  796224 
Change-Id: Iac3cfed3e4be5face023cd3d6db8d575d2b5a114
Reviewed-on: https://chromium-review.googlesource.com/843975
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527249}
[modify] https://crrev.com/f1a95e3cea56b7025baf0981fc831707b361f6af/components/autofill/ios/browser/resources/autofill_controller.js