Work on separate browser contexts

ui/aura/test/aura_test_helper.cc

 // Copyright (c) 2012 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 "ui/aura/test/aura_test_helper.h"
 
 #include "base/message_loop.h"
 #include "base/run_loop.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/env.h"
@@ skipping 58 matching lines @@
 
 void AuraTestHelper::TearDown() {
   teardown_called_ = true;
   test_input_method_.reset();
   stacking_client_.reset();
   test_activation_client_.reset();
   root_window_capture_client_.reset();
   focus_manager_.reset();
   root_window_.reset();
   test_screen_.reset();
+  gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, NULL);
   aura::Env::DeleteInstance();
 }
 
 void AuraTestHelper::RunAllPendingInMessageLoop() {
 #if !defined(OS_MACOSX)
   // TODO(jbates) crbug.com/134753 Find quitters of this RunLoop and have them
   //              use run_loop.QuitClosure().
   base::RunLoop run_loop(Env::GetInstance()->GetDispatcher());
   run_loop.RunUntilIdle();
 #endif
 }
 
 }  // namespace test
 }  // namespace aura