Currently, the app is installed here: https://cs.chromium.org/chromium/src/chromeos/services/multidevice_setup/multidevice_setup_impl.cc?q=InstallAndroidSmsApp

Instead, we should observer HostBackendDelegate and install the app once there is a host set on the back-end.

SGTM, Kyle. Do you suggest we just make MultiDeviceSetupImpl HostBackendDelegate Observer? That seems pretty straightforward to me, but I want to make sure you didn't haven some place else in mind.

I'd recommend just creating a new class instead which handles this case. MultiDeviceSetupImpl is more of a "glue" class which routes API requests to the relevant classes which handle those requests.

Check out how Josh created DeviceReenroller - it's initialized when MultiDeviceSetupImpl is created and handles those requests internally.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa

commit 3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa
Author: Jeremy Klein <jlklein@google.com>
Date: Fri Sep 28 01:12:54 2018

Install Messages PWA when host is set or verified.

This change moves the logic for installing the Android Messages PWA into
a helper class which is a HostStatusProvider::Observer. This allows it
to install the PWA when a host is set and also when signing into a new
Chromebook if the account already has a valid host.

Bug:  887775 
Change-Id: I1a1433b03010d391f9b8256754fc578dfb8a140b
Reviewed-on: https://chromium-review.googlesource.com/1248130
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Jeremy Klein <jlklein@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594943}
[modify] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/BUILD.gn
[add] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.cc
[add] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.h
[add] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer_unittest.cc
[modify] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/multidevice_setup_impl.cc
[modify] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/multidevice_setup_impl.h
[modify] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/multidevice_setup_impl_unittest.cc
[modify] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/public/cpp/fake_android_sms_app_helper_delegate.cc
[modify] https://crrev.com/3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa/chromeos/services/multidevice_setup/public/cpp/fake_android_sms_app_helper_delegate.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c1cd548c78d0a6138164568923b25fd22dfca4a6

commit c1cd548c78d0a6138164568923b25fd22dfca4a6
Author: Findit <findit-for-me@appspot.gserviceaccount.com>
Date: Fri Sep 28 05:44:53 2018

Revert "Install Messages PWA when host is set or verified."

This reverts commit 3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 594943 as the
culprit for failures in the build cycles as shown on:
https://findit-for-me.appspot.com/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtLzNlNjdkZjY0YmJmOTFkOGE3YjYxZDliZGYwYjBmMWVkZTNmMDViZmEM

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.memory/Linux%20ChromiumOS%20MSan%20Tests/8744

Sample Failed Step: chromeos_unittests

Original change's description:
> Install Messages PWA when host is set or verified.
> 
> This change moves the logic for installing the Android Messages PWA into
> a helper class which is a HostStatusProvider::Observer. This allows it
> to install the PWA when a host is set and also when signing into a new
> Chromebook if the account already has a valid host.
> 
> Bug:  887775 
> Change-Id: I1a1433b03010d391f9b8256754fc578dfb8a140b
> Reviewed-on: https://chromium-review.googlesource.com/1248130
> Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
> Commit-Queue: Jeremy Klein <jlklein@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#594943}

Change-Id: I7c249598402a82eaa23aca2e8c06acb429d9097c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  887775 
Reviewed-on: https://chromium-review.googlesource.com/1249737
Cr-Commit-Position: refs/heads/master@{#594994}
[modify] https://crrev.com/c1cd548c78d0a6138164568923b25fd22dfca4a6/chromeos/services/multidevice_setup/BUILD.gn
[delete] https://crrev.com/7d7da07a0ac455670057e76243e462b982937884/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.cc
[delete] https://crrev.com/7d7da07a0ac455670057e76243e462b982937884/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.h
[delete] https://crrev.com/7d7da07a0ac455670057e76243e462b982937884/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer_unittest.cc
[modify] https://crrev.com/c1cd548c78d0a6138164568923b25fd22dfca4a6/chromeos/services/multidevice_setup/multidevice_setup_impl.cc
[modify] https://crrev.com/c1cd548c78d0a6138164568923b25fd22dfca4a6/chromeos/services/multidevice_setup/multidevice_setup_impl.h
[modify] https://crrev.com/c1cd548c78d0a6138164568923b25fd22dfca4a6/chromeos/services/multidevice_setup/multidevice_setup_impl_unittest.cc
[modify] https://crrev.com/c1cd548c78d0a6138164568923b25fd22dfca4a6/chromeos/services/multidevice_setup/public/cpp/fake_android_sms_app_helper_delegate.cc
[modify] https://crrev.com/c1cd548c78d0a6138164568923b25fd22dfca4a6/chromeos/services/multidevice_setup/public/cpp/fake_android_sms_app_helper_delegate.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ae048b519f9bb43d9417705c6b07fa3045627aa6

commit ae048b519f9bb43d9417705c6b07fa3045627aa6
Author: Jeremy Klein <jlklein@google.com>
Date: Fri Sep 28 23:37:46 2018

Reland "Install Messages PWA when host is set or verified."

This is a reland of 3e67df64bbf91d8a7b61d9bdf0b0f1ede3f05bfa

Fixed the ASAN test by actually just removing some unnecessary code.

Original change's description:
> Install Messages PWA when host is set or verified.
>
> This change moves the logic for installing the Android Messages PWA into
> a helper class which is a HostStatusProvider::Observer. This allows it
> to install the PWA when a host is set and also when signing into a new
> Chromebook if the account already has a valid host.
>
> Bug:  887775 
> Change-Id: I1a1433b03010d391f9b8256754fc578dfb8a140b
> Reviewed-on: https://chromium-review.googlesource.com/1248130
> Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
> Commit-Queue: Jeremy Klein <jlklein@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#594943}

Bug:  887775 
Change-Id: I1941c20d7c31f8424f3d080db8e3580be01cd41f
Reviewed-on: https://chromium-review.googlesource.com/1252626
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Jeremy Klein <jlklein@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595250}
[modify] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/BUILD.gn
[add] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.cc
[add] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer.h
[add] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/android_sms_app_installing_status_observer_unittest.cc
[modify] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/multidevice_setup_impl.cc
[modify] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/multidevice_setup_impl.h
[modify] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/multidevice_setup_impl_unittest.cc
[modify] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/public/cpp/fake_android_sms_app_helper_delegate.cc
[modify] https://crrev.com/ae048b519f9bb43d9417705c6b07fa3045627aa6/chromeos/services/multidevice_setup/public/cpp/fake_android_sms_app_helper_delegate.h