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

ui/gfx/screen_aura.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 "base/logging.h"
-#include "ui/gfx/display.h"
-#include "ui/gfx/native_widget_types.h"
-#include "ui/gfx/screen_impl.h"
 
 namespace gfx {
 
-// gfx can't depend upon aura, otherwise we have circular dependencies. So,
-// gfx::Screen is pluggable and Desktop plugs in the real implementation.
-namespace {
-ScreenImpl* g_instance_ = NULL;
-}
-
-// static
-void Screen::SetInstance(ScreenImpl* screen) {
-  delete g_instance_;
-  g_instance_ = screen;
-}
-
-// static
-bool Screen::IsDIPEnabled() {
-  return true;
-}
-
-// static
-Point Screen::GetCursorScreenPoint() {
-  return g_instance_->GetCursorScreenPoint();
-}
-
-// static
-NativeWindow Screen::GetWindowAtCursorScreenPoint() {
-  return g_instance_->GetWindowAtCursorScreenPoint();
-}
-
-// static
-int Screen::GetNumDisplays() {
-  return g_instance_->GetNumDisplays();
-}
-
-// static
-Display Screen::GetDisplayNearestWindow(NativeView window) {
-  return g_instance_->GetDisplayNearestWindow(window);
-}
-
-// static
-Display Screen::GetDisplayNearestPoint(const Point& point) {
-  return g_instance_->GetDisplayNearestPoint(point);
-}
-
-// static
-Display Screen::GetDisplayMatching(const gfx::Rect& match_rect) {
-  return g_instance_->GetDisplayMatching(match_rect);
-}
-
-// static
-Display Screen::GetPrimaryDisplay() {
-  return g_instance_->GetPrimaryDisplay();
+Screen* CreateNativeScreen() {
+  NOTREACHED() << "Implementation should be installed at higher level.";
+  return NULL;
 }
 
 }  // namespace gfx