GitLab

Teach the browser to generate a WebAuthn challenge that is a SHA-256
hash over transaction data.

Also added a test page that automates expectation updating for the unit
test.

Bug: 1121020
Change-Id: Ic5515135eb8724eedc49d966f3986b0a48bbd519
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2381096
Commit-Queue: Danyao Wang <danyao@chromium.org>
Auto-Submit: Danyao Wang <danyao@chromium.org>
Reviewed-by: Adam Langley <agl@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802741}