[Autofill Assistant] Introduce CounterInput::ValidationRule.

This CL introduces the notion of validation for the CounterInput of the
FormAction. This allows to express multiple different validation rules
depending on the counters values.

Change-Id: I2a6c0cb684be3f7c8e98340b8682cac6d0f7531a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621918
Commit-Queue: Jordan Demeulenaere <jdemeulenaere@chromium.org>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Reviewed-by: Clemens Arbesser <arbesser@google.com>
Cr-Commit-Position: refs/heads/master@{#662637}
3 files changed