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This is another step toward out-of-process ash (go/mustash).

* Create the Widget in FirstRunController in chrome
* Move escape key handling into chrome
* Stop using OverlayEventFilter in ash. The old code wasn't actually
  relying on it for blocking event propagation, just for escape key
  handling and detecting screen lock and shutdown. The old code was
  also watching for LoginStatus changes, but that dates back to the
  use of OverlayEventFilter for partial screenshots (no longer used)
  and isn't relevant to first-run.
* Add mojo interfaces to tell ash to start/stop tutorial

Bug: 756057
Test: ash_unittests, browser_tests
Change-Id: Icfd88e3541f1393b6a2309120c74bbe6a69b967f
Reviewed-on: https://chromium-review.googlesource.com/1000395
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551147}