Enable DevToolsAutofillTest.TriggerCreditCardInIframe

The test was missing the kAutofillAcrossIframes feature
to work in the chrome branded builds. Non-chrome branded
builds have the feature enabled via the field trials config.
The feature will be soon turned on by default and the previous
autofill mode will be removed. Therefore, we can support only
this mode in CDP.

Fixed: 1445476
Change-Id: Ie4a9a1f3fe7ae67b283a861ff05010f049e4f597
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4562434


Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Alex Rudenko <alexrudenko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148911}