CL https://chromium-review.googlesource.com/c/chromium/src/+/1349589

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/da87860cb19a14c6bc35720bdff3355b84f64407

commit da87860cb19a14c6bc35720bdff3355b84f64407
Author: Antonio Gomes <tonikitoo@igalia.com>
Date: Mon Nov 26 14:22:37 2018

Convert arc_play_store_enabled_preference_handler_unittest.cc to use IdentityTestEnvironment

IdentityManager currently wraps other signin APIs including SigninManager
and PO2TS. This CL migrates ArcPlayStoreEnabledPreferenceHandlerTest
and IdentityManager's testing facility IdentityTestEnvironment, and
hides the test internals from SigninManager APIs.

This is part of the servicification effort.

BUG= 907484 

Change-Id: I85f764f3477ee8e974298c0b41e22ac6277f61c5
Reviewed-on: https://chromium-review.googlesource.com/c/1349589
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610843}
[modify] https://crrev.com/da87860cb19a14c6bc35720bdff3355b84f64407/chrome/browser/chromeos/arc/arc_play_store_enabled_preference_handler_unittest.cc