[Autofill Assistant] Fixed payment request divider visibility bug.

This fixes a bug where not all section dividers were initially visible. This CL also contains:
 - Refactoring to move all PR testing to Espresso, for better stability and consistency with other tests.
 - Added regression test for the above-mentioned bug.

Bug: b/133725664
Bug: 806868
Change-Id: Ic94a2aeb8158e2fa356bb0f235a3a1172ed9177c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660433
Commit-Queue: Clemens Arbesser <arbesser@google.com>
Reviewed-by: Stephane Zermatten <szermatt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669687}
7 files changed