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

ui/base/gtk/gtk_screen_util.h

Index: ui/base/gtk/gtk_screen_util.h
diff --git a/ui/base/gtk/gtk_screen_util.h b/ui/base/gtk/gtk_screen_util.h
index 312075081efcda30dc1a934de41f930221694ac8..b916cf238afd24cfea6e7c2fbdcfc7193a0ce1a3 100644
--- a/ui/base/gtk/gtk_screen_util.h
+++ b/ui/base/gtk/gtk_screen_util.h
@@ -10,6 +10,7 @@
 #include "ui/base/ui_export.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/rect.h"
+#include "ui/gfx/vector2d.h"
 
 namespace ui {
 
@@ -22,8 +23,8 @@ 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);