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This class is no longer needed because of the new WidgetDelegate
setters.

This change:
1) Replaces LockScreenWidgetDelegate with a plain WidgetDelegate
2) Refactors LockScreen::Show() to pass the contents view directly
   into the Widget factory method, in aid of (1)

Bug: 1075649
Change-Id: I5a89cbd822ad22aef62a76f6ea8afb70f6431d08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2458450
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814873}