Add Vector2d classes that represent offsets, instead of using Point.

ui/base/gtk/gtk_screen_util.h

 // 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_BASE_GTK_GTK_SCREEN_UTILS_H_
 #define UI_BASE_GTK_GTK_SCREEN_UTILS_H_
 
 #include <gtk/gtk.h>
 
 #include "ui/base/ui_export.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/rect.h"
+#include "ui/gfx/vector2d.h"
 
 namespace ui {
 
 // Returns true if the screen is composited, false otherwise.
 UI_EXPORT bool IsScreenComposited();
 
 // Get the current location of the mouse cursor relative to the screen.
 UI_EXPORT gfx::Point ScreenPoint(GtkWidget* widget);
 
 // Get the current location of the mouse cursor relative to the widget.
 UI_EXPORT gfx::Point ClientPoint(GtkWidget* widget);
 
-// Gets the position of a gtk widget in screen coordinates.
-UI_EXPORT gfx::Point GetWidgetScreenPosition(GtkWidget* widget);
+// Gets the offset of a gtk widget from the origin in screen coordinates.
+UI_EXPORT gfx::Vector2d GetWidgetScreenOffset(GtkWidget* widget);
 
 // Returns the bounds of the specified widget in screen coordinates.
 UI_EXPORT gfx::Rect GetWidgetScreenBounds(GtkWidget* widget);
 
 }  // namespace ui
 
 #endif  // UI_BASE_GTK_GTK_SCREEN_UTILS_H_