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

ui/gfx/vector2d_f.h

Index: ui/gfx/vector2d_f.h
diff --git a/ui/gfx/vector2d_f.h b/ui/gfx/vector2d_f.h
new file mode 100644
index 0000000000000000000000000000000000000000..e2baa0cc4a6201cefcfe1689ec2fd24586046f19
--- /dev/null
+++ b/ui/gfx/vector2d_f.h
@@ -0,0 +1,81 @@
+// 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.
+
+// Defines a simple float vector class.  This class is used to indicate a
+// distance in two dimensions between two points. Subtracting two points should
+// produce a vector, and adding a vector to a point produces the point at the
+// vector's distance from the original point.
+
+#ifndef UI_GFX_VECTOR2D_F_H_
+#define UI_GFX_VECTOR2D_F_H_
+
+#include <string>
+
+#include "ui/base/ui_export.h"
+
+namespace gfx {
+
+class UI_EXPORT Vector2dF {
+ public:
+  Vector2dF();
+  Vector2dF(float x, float y);
+
+  float x() const { return x_; }
+  void set_x(float x) { x_ = x; }
+
+  float y() const { return y_; }
+  void set_y(float y) { y_ = y; }
+
+  // True if both components of the vector are 0.
+  bool IsZero() const;
+
+  // Add the components of the |other| vector to the current vector.
+  void Add(const Vector2dF& other);
+  // Subtract the components of the |other| vector from the current vector.
+  void Subtract(const Vector2dF& other);
+
+  void operator+=(const Vector2dF& other) { Add(other); }
+  void operator-=(const Vector2dF& other) { Subtract(other); }
+
+  // Gives the square of the diagonal length of the vector.
+  double LengthSquared() const;
+  // Gives the diagonal length of the vector.
+  float Length() const;
+
+  // Scale the x and y components of the vector by |scale|.
+  void Scale(float scale) { Scale(scale, scale); }
+  // Scale the x and y components of the vector by |x_scale| and |y_scale|
+  // respectively.
+  void Scale(float x_scale, float y_scale);
+
+  std::string ToString() const;
+
+ private:
+  float x_;
+  float y_;
+};
+
+inline bool operator==(const Vector2dF& lhs, const Vector2dF& rhs) {
+  return lhs.x() == rhs.x() && lhs.y() == rhs.y();
+}
+
+inline Vector2dF operator-(const Vector2dF& v) {
+  return Vector2dF(-v.x(), -v.y());
+}
+
+inline Vector2dF operator+(const Vector2dF& lhs, const Vector2dF& rhs) {
+  Vector2dF result = lhs;
+  result.Add(rhs);
+  return result;
+}
+
+inline Vector2dF operator-(const Vector2dF& lhs, const Vector2dF& rhs) {
+  Vector2dF result = lhs;
+  result.Add(-rhs);
+  return result;
+}
+
+}  // namespace gfx
+
+#endif // UI_GFX_VECTOR2D_F_H_