mustash: Convert TraySupervisedUserTest to AshTest

ash/common/test/test_system_tray_delegate.h

Index: ash/common/test/test_system_tray_delegate.h
diff --git a/ash/common/test/test_system_tray_delegate.h b/ash/common/test/test_system_tray_delegate.h
index 3f5ca4aceaee9e0804283cc4afbab2860af525b5..29c0dd30514fbdeaa15bb3171d0482db9e616101 100644
--- a/ash/common/test/test_system_tray_delegate.h
+++ b/ash/common/test/test_system_tray_delegate.h
@@ -25,9 +25,8 @@ class TestSystemTrayDelegate : public DefaultSystemTrayDelegate {
 
   // Changes the login status when initially the delegate is created. This will
   // be called before AshTestBase::SetUp() to test the case when chrome is
-  // restarted right after the login (such like a flag is set).
-  // This value will be reset in AshTestHelper::TearDown,  most test fixtures
-  // don't need to care its lifecycle.
+  // restarted right after the login (such like a flag is set). Tests must reset
+  // to LoginStatus::USER after they complete.
   static void SetInitialLoginStatus(LoginStatus login_status);
 
   // Changes the current login status in the test. This also invokes