Introduce BubbleControllerBase class

BubbleControllerBase is meant to be the base class for Autofill and
Passwords bubble controllers. This CL introduces this class and
currently AutofillBubbleControllerBase extends it.
In further CLs, ManagerPasswordsUIController will also extend this
class.

Bug: 43242960
Change-Id: I86d2c25ccf1d7191f336f9827a79a8e341e8a853
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6818378
Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Vidhan Jain <vidhanj@google.com>
Cr-Commit-Position: refs/heads/main@{#1496533}