Move Screen, its impls, DisplayObserver and DisplayChangeNotifier to ui/display

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::GetScreen()->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::GetScreen()->GetNumDisplays(), 1);
-}
-
-}  // namespace