Makes a couple of tests reset state appropriately

content/browser/renderer_host/input/touch_emulator_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 <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/time/time.h"
@@ skipping 44 matching lines @@
     emulator_.reset(new TouchEmulator(this));
     emulator_->Enable(ui::GestureProviderConfigType::GENERIC_MOBILE);
   }
 
   void TearDown() override {
     emulator_->Disable();
     EXPECT_EQ("", ExpectedEvents());
 
 #if defined(USE_AURA)
     aura::Env::DeleteInstance();
+    gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, nullptr);
     screen_.reset();
 #endif
   }
 
   void ForwardGestureEvent(const blink::WebGestureEvent& event) override {
     forwarded_events_.push_back(event.type);
   }
 
   void ForwardEmulatedTouchEvent(const blink::WebTouchEvent& event) override {
     forwarded_events_.push_back(event.type);
@@ skipping 470 matching lines @@
   MouseDown(100, 200);
   EXPECT_EQ("TouchStart GestureTapDown", ExpectedEvents());
   MouseUp(200, 200);
   EXPECT_EQ(
       "TouchMove GestureTapCancel GestureScrollBegin GestureScrollUpdate"
       " TouchEnd GestureScrollEnd",
       ExpectedEvents());
 }
 
 }  // namespace content