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

ui/gfx/point.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_GFX_POINT_H_
 #define UI_GFX_POINT_H_
 
 #include "ui/base/ui_export.h"
 #include "ui/gfx/point_base.h"
 #include "ui/gfx/point_f.h"
+#include "ui/gfx/vector2d.h"
 
 #if defined(OS_WIN)
 typedef unsigned long DWORD;
 typedef struct tagPOINT POINT;
 #elif defined(OS_IOS)
 #include <CoreGraphics/CoreGraphics.h>
 #elif defined(OS_MACOSX)
 #include <ApplicationServices/ApplicationServices.h>
 #endif
 
 namespace gfx {
 
 // A point has an x and y coordinate.
-class UI_EXPORT Point : public PointBase<Point, int> {
+class UI_EXPORT Point : public PointBase<Point, int, Vector2d> {
  public:
   Point();
   Point(int x, int y);
 #if defined(OS_WIN)
   // |point| is a DWORD value that contains a coordinate.  The x-coordinate is
   // the low-order short and the y-coordinate is the high-order short.  This
   // value is commonly acquired from GetMessagePos/GetCursorPos.
   explicit Point(DWORD point);
   explicit Point(const POINT& point);
   Point& operator=(const POINT& point);
@@ skipping 26 matching lines @@
 };
 
 inline bool operator==(const Point& lhs, const Point& rhs) {
   return lhs.x() == rhs.x() && lhs.y() == rhs.y();
 }
 
 inline bool operator!=(const Point& lhs, const Point& rhs) {
   return !(lhs == rhs);
 }
 
-inline Point operator+(Point lhs, Point rhs) {
+inline Point operator+(const Point& lhs, const Vector2d& rhs) {
   return lhs.Add(rhs);
 }
 
-inline Point operator-(Point lhs, Point rhs) {
+inline Point operator-(const Point& lhs, const Vector2d& rhs) {
   return lhs.Subtract(rhs);
 }
 
+inline Vector2d operator-(const Point& lhs, const Point& rhs) {
+  return lhs.OffsetFrom(rhs);
+}
+
+inline Point PointAtOffsetFromOrigin(const Vector2d& offset_from_origin) {
+  return Point(offset_from_origin.x(), offset_from_origin.y());
+}
+
 #if !defined(COMPILER_MSVC)
-extern template class PointBase<Point, int>;
+extern template class PointBase<Point, int, Vector2d>;
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_POINT_H_