[Autofill] Create new UI classes for the Autofill Dropdown on Android.

This code changes no behavior. It's simply in preparation for changing
the autofill dropdown in the next CLs.

Change-Id: I682c245d728c8bf3e8d5c57139b02e28a326111a
Reviewed-on: https://chromium-review.googlesource.com/1147428
Commit-Queue: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578332}
6 files changed