Enable Payment Request in WebView Shell

Before this patch, WebView shell would not be able to invoke locally
installed payment apps, because that requires enabling the Payment
Request API setting.

This patch enables the Payment Request API setting in WebView shell in
accordance with the documentation in:
https://developer.chrome.com/docs/android/payments-in-webviews

After this patch, a developer can navigate WebView shell to
https://rsolomakhin.github.io/pr/payjs-test/ and complete a test payment
using Google Pay.

Fixed: 406227441
Change-Id: I6631486247d17bce4a9458c6da8f71f57bdab5b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6657063
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1476416}