The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4f047de699e30cc02af610a565326e7046245187

commit 4f047de699e30cc02af610a565326e7046245187
Author: gogerald <gogerald@google.com>
Date: Tue Mar 27 00:48:07 2018

[Payments] Add a use counter to number of PaymentRequest.show without gesture

Bug: 825270
Change-Id: I978f26cbfbefa48c0c4b1dffe64d49d750749db6
Reviewed-on: https://chromium-review.googlesource.com/977950
Reviewed-by: Luna Lu <loonybear@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545911}
[modify] https://crrev.com/4f047de699e30cc02af610a565326e7046245187/chrome/browser/page_load_metrics/observers/use_counter/ukm_features.cc
[modify] https://crrev.com/4f047de699e30cc02af610a565326e7046245187/third_party/WebKit/Source/modules/payments/PaymentRequest.cpp
[modify] https://crrev.com/4f047de699e30cc02af610a565326e7046245187/third_party/WebKit/public/platform/web_feature.mojom
[modify] https://crrev.com/4f047de699e30cc02af610a565326e7046245187/tools/metrics/histograms/enums.xml

<0.006% of users would be affected by this change.

Should be OK to start requiring user gesture after the show() promise is implemented.