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This change updates the WebOTP API shape to the latest spec.
It adds the following changes.

1. Adds `code` field for the one-time-code
2. Updates `id` to be undefined for OTPCredentials
3. Updates OtpCredentials to be OTPCredentials

WebOTP Explainer: https://github.com/samuelgoto/WebOTP/blob/master/explainer.md

Bug: 1053594
Change-Id: I747446b2fffc8f00afef105db3a5bcb35b124890
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2068300Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Ayu Ishii <ayui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745092}