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

ui/gfx/screen.cc

+// Copyright 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 "base/logging.h"
+#include "ui/gfx/screen.h"
+#include "ui/gfx/screen_type_delegate.h"
+
+namespace gfx {
+
+Screen* g_screen_[SCREEN_TYPE_LAST + 1];
+ScreenTypeDelegate* g_screen_type_delegate_;
+
+Screen::Screen() {
+}
+
+Screen::~Screen() {
+}
+
+// static
+Screen* Screen::GetScreenFor(NativeView view) {
+  ScreenType type = SCREEN_TYPE_NATIVE;
+  if (g_screen_type_delegate_)
+    type = g_screen_type_delegate_->GetScreenTypeForNativeView(view);
+  if (type == SCREEN_TYPE_NATIVE)
+    return GetNativeScreen();
+  DCHECK(g_screen_[type]);
+  return g_screen_[type];
+}
+
+// static
+void Screen::SetScreenInstance(ScreenType type, Screen* instance) {
+  g_screen_[type] = instance;
+}
+
+// static
+void Screen::SetScreenTypeDelegate(ScreenTypeDelegate* delegate) {
+  g_screen_type_delegate_ = delegate;
+}
+
+// static
+Screen* Screen::GetNativeScreen() {
+  if (!g_screen_[SCREEN_TYPE_NATIVE])
+    g_screen_[SCREEN_TYPE_NATIVE] = CreateNativeScreen();
+  return g_screen_[SCREEN_TYPE_NATIVE];
+}
+
+}