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Changes:
1, make init screen focusable so as to read it's content for accessibility
2, announce first run experience is shown and autofill assistant is available
3, announce autofill assistant message
4, do not show autofill assistant bottom bar when showing init screen.
5, move the functions around in controller.cc to match their declaration order.

Bug: 806868
Change-Id: I7376ef905d3e7dc7f9949557f1307cb07ed28c95
Reviewed-on: https://chromium-review.googlesource.com/c/1351649
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611490}