TestScreen shouldn't be marked aura export

ui/gfx/screen.h

Index: ui/gfx/screen.h
diff --git a/ui/gfx/screen.h b/ui/gfx/screen.h
index cd363b366985b4a519c0a3784875a9b5fcf3d25f..a451130216815d063dbf266deef258f4339dbebb 100644
--- a/ui/gfx/screen.h
+++ b/ui/gfx/screen.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -20,7 +20,7 @@ class UI_EXPORT Screen {
  public:
   virtual ~Screen() {}
 
-#if defined(USE_AURA)
+#if defined(USE_ASH)
   // Sets the instance to use. This takes owernship of |screen|, deleting the
   // old instance. This is used on aura to avoid circular dependencies between
   // ui and aura.