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

ui/gfx/vector2d_f.cc

+// 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.
+
+#include "base/stringprintf.h"
+#include "ui/gfx/vector2d_f.h"
+
+namespace gfx {
+
+Vector2dF::Vector2dF()
+    : m_x(0),
+      m_y(0) {
+}
+
+Vector2dF::Vector2dF(float x, float y)
+    : m_x(x),
+      m_y(y) {
+}
+
+std::string Vector2dF::ToString() const {
+  return base::StringPrintf("[%f %f]", m_x, m_y);
+}
+
+}  // namespace gfx