Fix flakiness in ProfileProviderTest by shutting down LoginState

Bug: 939160
Change-Id: Ib7dd41dc550ffa712720cc633aa7585e4f4d6d79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506451Reviewed-by: Gabriel Marin <gmx@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638404}

chrome/browser/metrics/perf/profile_provider_chromeos_unittest.cc

@@ -140,6 +140,7 @@ class ProfileProviderTest : public testing::Test {
   void TearDown() override {
     profile_provider_.reset();
     chromeos::PowerManagerClient::Shutdown();
+    chromeos::LoginState::Shutdown();
   }
 
  protected: