Aura/ash: On Desktops, use a aura::client to resolve screen coordinates.

ui/aura/client/screen_position_client.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/aura/client/screen_position_client.h"
+
+#include "ui/aura/window.h"
+#include "ui/aura/window_property.h"
+
+DECLARE_WINDOW_PROPERTY_TYPE(aura::client::ScreenPositionClient*)
+
+namespace aura {
+namespace client {
+
+DEFINE_LOCAL_WINDOW_PROPERTY_KEY(ScreenPositionClient*,
+                                 kScreenPositionClientKey,
+                                 NULL);
+
+void SetScreenPositionClient(Window* window,
+                             ScreenPositionClient* client) {
+  window->SetProperty(kScreenPositionClientKey, client);
+}
+
+ScreenPositionClient* GetScreenPositionClient(Window* window) {
+  return window ? window->GetProperty(kScreenPositionClientKey) : NULL;
+}
+
+}  // namespace client
+}  // namespace aura