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

ui/gfx/rect.h

Index: ui/gfx/rect.h
diff --git a/ui/gfx/rect.h b/ui/gfx/rect.h
index 2eab239d4bc76d948c93b86606622841fe778b39..2dffb57317e9f65d1189f864c0ba2adda71425a9 100644
--- a/ui/gfx/rect.h
+++ b/ui/gfx/rect.h
@@ -33,7 +33,8 @@ namespace gfx {
 
 class Insets;
 
-class UI_EXPORT Rect : public RectBase<Rect, Point, Size, Insets, int> {
+class UI_EXPORT Rect
+    : public RectBase<Rect, Point, Size, Insets, Vector2d, int> {
  public:
   Rect();
   Rect(int width, int height);
@@ -76,7 +77,7 @@ inline bool operator!=(const Rect& lhs, const Rect& rhs) {
 }
 
 #if !defined(COMPILER_MSVC)
-extern template class RectBase<Rect, Point, Size, Insets, int>;
+extern template class RectBase<Rect, Point, Size, Insets, Vector2d, int>;
 #endif
 
 }  // namespace gfx