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- 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}