Makes a couple of tests reset state appropriately

chrome/browser/signin/signin_error_notifier_ash_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/signin/signin_error_notifier_ash.h"
 
 #include "ash/test/ash_test_base.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/notifications/notification.h"
@@ skipping 62 matching lines @@
         new TestingProfileManager(TestingBrowserProcess::GetGlobal()));
     ASSERT_TRUE(profile_manager_->SetUp());
 
     TestingBrowserProcess::GetGlobal();
     AshTestBase::SetUp();
 
     // Set up screen for Windows.
 #if defined(OS_WIN)
     test_screen_.reset(aura::TestScreen::Create(gfx::Size()));
     gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, test_screen_.get());
-    gfx::Screen::SetScreenTypeDelegate(new ScreenTypeDelegateDesktop);
+    gfx::Screen::SetScreenTypeDelegate(&screen_type_delegate_);
 #endif
 
     error_controller_ = SigninErrorControllerFactory::GetForProfile(
         profile_.get());
     SigninErrorNotifierFactory::GetForProfile(profile_.get());
     notification_ui_manager_ = g_browser_process->notification_ui_manager();
   }
 
   void TearDown() override {
 #if defined(OS_WIN)
+    gfx::Screen::SetScreenTypeDelegate(nullptr);
+    gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, nullptr);
     test_screen_.reset();
 #endif
     profile_manager_.reset();
 
     AshTestBase::TearDown();
   }
 
  protected:
   void GetMessage(base::string16* message) {
     const Notification* notification =
         g_browser_process->notification_ui_manager()->FindById(
             kNotificationId,
             NotificationUIManager::GetProfileID(profile_.get()));
     ASSERT_FALSE(notification == NULL);
     *message = notification->message();
   }
 
 #if defined(OS_WIN)
+  ScreenTypeDelegateDesktop screen_type_delegate_;
   scoped_ptr<gfx::Screen> test_screen_;
 #endif
   scoped_ptr<TestingProfileManager> profile_manager_;
   scoped_ptr<TestingProfile> profile_;
   SigninErrorController* error_controller_;
   NotificationUIManager* notification_ui_manager_;
 };
 
 TEST_F(SigninErrorNotifierTest, NoErrorAuthStatusProviders) {
   ASSERT_FALSE(notification_ui_manager_->FindById(
@@ skipping 127 matching lines @@
       EXPECT_FALSE(notification->title().empty());
       EXPECT_FALSE(notification->message().empty());
       EXPECT_EQ((size_t)1, notification->buttons().size());
     }
   }
 }
 #endif
 
 }  // namespace test
 }  // namespace ash