We also should not install if the feature is unsupported by the Chromebook or by the phone.

Additionally, we need to add a listener for when this state changes. For instance, imagine that you go through setup with the Messages flag off, then you turn it on later. Currently, the app is only installed when you complete setup, so it would not be installed after turning the flag on.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c2945c982be854b7f0ed315b2b45e05264a072d5

commit c2945c982be854b7f0ed315b2b45e05264a072d5
Author: Jeremy Klein <jlklein@google.com>
Date: Mon Oct 01 16:45:45 2018

Only install Messages PWA when supported and allowed.

Avoid installing the Android Messages PWA if prohibited by policy or if
either the phone or Chromebook does not support it. Also listen for
changes in feature state to install the app if something changes.

Bug:  884290 
Change-Id: I527828e68c3578e54a1ce15cace64e4ed2c81745
Reviewed-on: https://chromium-review.googlesource.com/1250209
Commit-Queue: Jeremy Klein <jlklein@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595466}
[modify] https://crrev.com/c2945c982be854b7f0ed315b2b45e05264a072d5/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.cc
[modify] https://crrev.com/c2945c982be854b7f0ed315b2b45e05264a072d5/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.h
[modify] https://crrev.com/c2945c982be854b7f0ed315b2b45e05264a072d5/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer_unittest.cc
[modify] https://crrev.com/c2945c982be854b7f0ed315b2b45e05264a072d5/chromeos/services/multidevice_setup/multidevice_setup_impl.cc
[modify] https://crrev.com/c2945c982be854b7f0ed315b2b45e05264a072d5/chromeos/services/multidevice_setup/multidevice_setup_impl_unittest.cc