[M73 merge] assistant: Start OOBE for new users

If a new device receives Assistant feature after system image update,
they don't know the feature exists and we need a way to have the user
know and enable the feature.  One option is to show the Assistant OOBE
in this case.  We have a pref that marks the OOBE has shown
kVoiceInteractionActivityControlAccepted. We can check if this value is
null and show the OOBE in assistant_setup.

TBR=xiyuan@chromium.org, xiaohuic@chromium.org

(cherry picked from commit 440570664394e6675fad93fe49f7d5b7c156d9b5)

Bug: 926612, b/122851527
Test: manual
Change-Id: I38dbe44a85496d4abde8ae28ade158aa9382ad87
Reviewed-on: https://chromium-review.googlesource.com/c/1444699
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#627849}
Reviewed-on: https://chromium-review.googlesource.com/c/1450755
Cr-Commit-Position: refs/branch-heads/3683@{#136}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
6 files changed