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This is a reland of 8411cc66

Original change's description:
> OOBE - Improve reset screen confirmation dialog
> 
> - Replace the dialog on the reset screen with the oobe-help-dialog
>   that complies with UX specs and reuses available code.
> 
> - Refactor the confirmation dialog logic so that it lives in the
>   main element 'oobe-reset'.
> 
> - Remove the intermediate oobe_reset_screen by using LoginScreenBehavior
> 
> - Add a waiter to test::OobeJS for waiting upon the presence of an
>   attribute. Such as waiting on the 'open' attribute of dialogs.
> 
> - Add constants and modifications to the browser tests of the reset
>   screen.
> 
> Fixed: 933310
> Change-Id: I54001745326b60ab5a0a19519923c54dffa5baec
> Bug: 933310
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2041474
> Commit-Queue: Renato Silva <rrsilva@google.com>
> Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
> Auto-Submit: Renato Silva <rrsilva@google.com>
> Cr-Commit-Position: refs/heads/master@{#744288}

Bug: 933310
Change-Id: I12aca96e98373beda746fc92f3d06cb6d1e86c72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2072383
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744604}