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This enables UserAuthenticationServiceProvider to call
AuthDialogController to start the dialog. Currently the dialog
only has a dev view which will only show when a command line
switch is enabled.

TEST=Used u2fd to call UserAuthenticationServiceProvider while
     having --show-auth-dialog-dev-overlap. Observed that the debug
     view shows up.

Bug: b:156258540
Change-Id: Ibe4437c628fb5aed91b63e7905518112ce97a4b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298544
Commit-Queue: Yicheng Li <yichengli@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797929}