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

ui/gfx/vector2d_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.
+
+// Defines a simple float vector class.  This class is used to indicate a
+// distance in two dimentions 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 m_x; }
+  void set_x(float x) { m_x = x; }
+
+  float y() const { return m_y; }
+  void set_y(float y) { m_y = y; }
+
+  void Grow(float x, float y) {
+    m_x += x;
+    m_y += y;
+  }
+
+  void Add(const Vector2dF& other) {
+    m_x += other.m_x;
+    m_y += other.m_y;
+  }
+
+  std::string ToString() const;
+
+ private:
+  float m_x;

[tfarina, 2012/10/25 00:40:20]

nit: please remember that we are in chromium code, not WebKit land :)

s/m_x/x_

+  float m_y;
+};
+
+inline Vector2dF operator-(const Vector2dF& v) {
+  return Vector2dF(-v.x(), -v.y());
+}
+
+}  // namespace gfx
+
+#endif // UI_GFX_VECTOR2D_F_H_