Please test.

I am able to reproduce this. In any of the text fields of Payments screen, the sybmol is converted into emoji.
Works fine in Omnibox, AutofillSettings Text fields.

Please let me know if you need any other information.

https://drive.google.com/file/d/1E5WCXM_R3aCEydHUgDIxoyq0nlDSA4jb/view

Device: iPhone7 plus, iOS: 11.2.2
Keyboard: Japanese Keyboard
Chrome: M65 canary

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4af8458721cdfcb5aa83011e154960a0e4020987

commit 4af8458721cdfcb5aa83011e154960a0e4020987
Author: Mohamad Ahmadi <mahmadi@chromium.org>
Date: Tue Feb 13 23:07:07 2018

[PR] Fixes the bug when typing sonant mark (Japanese) in Payment Request UI

Fixes the issue by return early from UITextFieldDelegate's
textField:shouldChangeCharactersInRange:replacementString: when no
formatting is necessary.
Allowing the speficied text range to be replaced (rather than changing the
textfield's value manually) allows the keyboard to change in order to
type the sonant mark.
Formatting is generally required for fields with numerical valuees (e.g.,
CC number and phone number). Typing the sonant mark is not supported in
those cases.

Bug:  806272 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I58c10e05bdf9508883bdf00f4a1f03de486a9aeb
Reviewed-on: https://chromium-review.googlesource.com/899107
Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536534}
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/chrome/browser/ui/payments/address_edit_mediator.mm
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/chrome/browser/ui/payments/contact_info_edit_mediator.mm
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/chrome/browser/ui/payments/credit_card_edit_mediator.mm
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/chrome/browser/ui/payments/payment_request_edit_view_controller.mm
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/chrome/browser/ui/payments/payment_request_edit_view_controller_data_source.h
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/chrome/browser/ui/payments/payment_request_edit_view_controller_unittest.mm
[modify] https://crrev.com/4af8458721cdfcb5aa83011e154960a0e4020987/ios/showcase/payments/sc_payments_editor_coordinator.mm

Verified in 66.0.3351.0 Canary, iPhone 7 iOS11
Looks good