Clean up of password dialog ui code -

Split dialog classes and webuis into two different files.
Added a new little class BasePasswordDialog that has the code common to all 3 dialogs.

Bug: 930109
Change-Id: I7c6d407a1eec2fdd297f9943d0119b2b0bc85b0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1718805
Commit-Queue: A Olsen <olsen@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681233}