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

ui/gfx/point_f.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_F_H_
 #define UI_GFX_POINT_F_H_
 
 #include <string>
 
 #include "ui/base/ui_export.h"
 #include "ui/gfx/point_base.h"
+#include "ui/gfx/vector2d_f.h"
 
 namespace gfx {
 
 // A floating version of gfx::Point.
-class UI_EXPORT PointF : public PointBase<PointF, float> {
+class UI_EXPORT PointF : public PointBase<PointF, float, Vector2dF> {
  public:
   PointF();
   PointF(float x, float y);
   ~PointF();
 
   PointF Scale(float scale) const WARN_UNUSED_RESULT {
     return Scale(scale, scale);
   }
 
   PointF Scale(float x_scale, float y_scale) const WARN_UNUSED_RESULT {
     return PointF(x() * x_scale, y() * y_scale);
   }
 
   // Returns a string representation of point.
   std::string ToString() const;
 };
 
 inline bool operator==(const PointF& lhs, const PointF& rhs) {
   return lhs.x() == rhs.x() && lhs.y() == rhs.y();
 }
 
 inline bool operator!=(const PointF& lhs, const PointF& rhs) {
   return !(lhs == rhs);
 }
 
-inline PointF operator+(PointF lhs, PointF rhs) {
+inline PointF operator+(const PointF& lhs, const Vector2dF& rhs) {
   return lhs.Add(rhs);
 }
 
-inline PointF operator-(PointF lhs, PointF rhs) {
+inline PointF operator-(const PointF& lhs, const Vector2dF& rhs) {
   return lhs.Subtract(rhs);
 }
 
+inline Vector2dF operator-(const PointF& lhs, const PointF& rhs) {
+  return lhs.OffsetFrom(rhs);
+}
+
+inline PointF PointAtOffsetFromOrigin(const Vector2dF& offset_from_origin) {
+  return PointF(offset_from_origin.x(), offset_from_origin.y());
+}
+
 #if !defined(COMPILER_MSVC)
-extern template class PointBase<PointF, float>;
+extern template class PointBase<PointF, float, Vector2dF>;
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_POINT_F_H_