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

ui/aura/client/screen_position_client.h

Index: ui/aura/client/screen_position_client.h
diff --git a/ui/aura/client/screen_position_client.h b/ui/aura/client/screen_position_client.h
new file mode 100644
index 0000000000000000000000000000000000000000..bca59c76d8505607cd1be4d6f0d9555237cf7e05
--- /dev/null
+++ b/ui/aura/client/screen_position_client.h
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+// 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.
+
+#ifndef UI_AURA_SCREEN_POSITION_CLIENT_H_
+#define UI_AURA_SCREEN_POSITION_CLIENT_H_
+#pragma once
+
+#include "ui/aura/aura_export.h"
+#include "ui/aura/window.h"
+
+namespace aura {
+
+class Event;
+class Window;
+
+namespace client {
+
+// An interface implemented by an object that changes coordinates on a
+// RootWindow into system coordinates.
+class AURA_EXPORT ScreenPositionClient {
+ public:
+  // Converts the |screen_point| from a given RootWindow's coordinates space
+  // into screen coordinate space.
+  virtual void ConvertToScreenPoint(gfx::Point* screen_point) = 0;
+
+  virtual ~ScreenPositionClient() {}
+};
+
+// Sets/Gets the activation client on the Window.
+AURA_EXPORT void SetScreenPositionClient(Window* window,
+                                         ScreenPositionClient* client);
+AURA_EXPORT ScreenPositionClient* GetScreenPositionClient(
+    Window* window);
+
+}  // namespace clients
+}  // namespace aura
+
+#endif  // UI_AURA_SCREEN_POSITION_CLIENT_H_