GitLab

Clean up before making it work with out-of-process ash (go/mustash).

* Make FirstRunHelper a concrete class
* Eliminate ash::Shell::CreateFirstRunHelper
* Move some methods to FirstRunController in chrome

Bug: 756057
Test: existing ash_unittests, browser_tests
Change-Id: I6d3660f64e2184a03c2f92b204200a26b5f7dab8
Reviewed-on: https://chromium-review.googlesource.com/990725Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547557}