GitLab

DialogModel is a currently unnecessary pure abstract class. Removing it simplifies the dialog
hierarchy.

Change-Id: Iac8c096b2879d594a723c57abcb1a05bba216e4b
Reviewed-on: https://chromium-review.googlesource.com/c/1345212Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613220}