[PR] EG tests for the PaymentDetailsModifier

- Also adds the kWebPaymentsModifiers feature flag to
  PaymentRequest::GetApplicableModifier() in order to be able to disable
  the feature through Finch.

Bug: 602666
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I24ae607e32eac253a7e5aa3efca4b01a36dfda58
Reviewed-on: https://chromium-review.googlesource.com/726530
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Marc-Antoine Courteau <macourteau@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#510652}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 05c18dfd9688b3736184c9e2cf65606e345d42ce
6 files changed