[Autofill Assistant] Wait until the page become interactive before scroll for focus

Make the focus element action as the click action to wait for the page to become interactive,
This potentially fix the issue, http://b/119665284

May add a browser test to simulate non-interactive situation

Change-Id: I88f4f033ffeeadcdd585839956f3c4861fbc29da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538981
Commit-Queue: Mathias Carlen <mcarlen@chromium.org>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Auto-Submit: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644352}
2 files changed