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..8f4f11b24e1e6ba82ab2a4d9c00e01ce7dd2236d 100644
--- a/ash/common/test/test_system_tray_delegate.h
+++ b/ash/common/test/test_system_tray_delegate.h
@@ -23,13 +23,6 @@ class TestSystemTrayDelegate : public DefaultSystemTrayDelegate {
   // AshTestHelper::TearDown.
   static void SetSystemUpdateRequired(bool required);
 
-  // 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.
-  static void SetInitialLoginStatus(LoginStatus login_status);
-
   // Changes the current login status in the test. This also invokes
   // UpdateAfterLoginStatusChange(). Usually this is called in the test code to
   // set up a login status. This will fit to most of the test cases, but this
@@ -70,6 +63,20 @@ class TestSystemTrayDelegate : public DefaultSystemTrayDelegate {
   DISALLOW_COPY_AND_ASSIGN(TestSystemTrayDelegate);
 };
 
+// Changes the initial login status before TestSystemTrayDelegate is created.
+// Allows testing the case when chrome is restarted right after login (such as a

[msw, 2016/10/14 16:10:29]

nit: "such as when a flag is set" or some better wording.

[James Cook, 2016/10/14 16:32:53]

Done.

+// flag is set).
+class ScopedInitialLoginStatus {
+ public:
+  explicit ScopedInitialLoginStatus(LoginStatus status);
+  ~ScopedInitialLoginStatus();
+
+ private:
+  LoginStatus old_status_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedInitialLoginStatus);
+};
+
 }  // namespace test
 }  // namespace ash