Simplify ManagePasswordsUIProvider code [1/5]

This introduces a new interface, GooglePasswordManagerUIProvider,
aiming to replace the current ManagePasswordsUIProvider code, but
with a narrower scope.

Bug: 912143
Change-Id: Ia11d8a20195d0bddc6806866096b523681ccc22a
Reviewed-on: https://chromium-review.googlesource.com/c/1367646
Commit-Queue: Ioana Pandele <ioanap@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620667}
3 files changed