Add context to gfx::Screen calls in support of simultaneous desktop+ash

ui/gfx/screen_unittest.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/gfx/screen.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
 TEST(ScreenTest, GetPrimaryDisplaySize) {
   // We aren't actually testing that it's correct, just that it's sane.
-  const gfx::Size size = gfx::Screen::GetPrimaryDisplay().size();
+  const gfx::Size size =
+      gfx::Screen::GetNativeScreen()->GetPrimaryDisplay().size();
   EXPECT_GE(size.width(), 1);
   EXPECT_GE(size.height(), 1);
 }
 
 TEST(ScreenTest, GetNumDisplays) {
   // We aren't actually testing that it's correct, just that it's sane.
-  EXPECT_GE(gfx::Screen::GetNumDisplays(), 1);
+  EXPECT_GE(gfx::Screen::GetNativeScreen()->GetNumDisplays(), 1);
 }
 
 }  // namespace