TestScreen shouldn't be marked aura export

ui/views/test/views_test_base.cc

Index: ui/views/test/views_test_base.cc
diff --git a/ui/views/test/views_test_base.cc b/ui/views/test/views_test_base.cc
index f12c26bd1ac6e7f811c76d926c8243f6be2138da..7b87f2e9e16bc7e17ae4c1abfd41c27a8c1137e3 100644
--- a/ui/views/test/views_test_base.cc
+++ b/ui/views/test/views_test_base.cc
@@ -14,6 +14,7 @@
 #include "ui/aura/env.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/test/test_activation_client.h"
+#include "ui/aura/test/test_screen.h"
 #include "ui/aura/test/test_stacking_client.h"
 #include "ui/base/ime/input_method.h"
 
@@ -88,6 +89,7 @@ void ViewsTestBase::SetUp() {
     views_delegate_.reset(new TestViewsDelegate());
 #if defined(USE_AURA)
   root_window_.reset(new aura::RootWindow);
+  gfx::Screen::SetInstance(new aura::TestScreen(root_window_.get()));
   root_window_->SetProperty(
       aura::client::kRootWindowInputMethodKey,
       test_input_method_.get());