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

ui/gfx/size.h

Index: ui/gfx/size.h
diff --git a/ui/gfx/size.h b/ui/gfx/size.h
index 4425207a18fa4b25b3a8bb433a4bd7b9da9940a8..d9eee533ab38220b0a7d1b187476783f9d6e4dcb 100644
--- a/ui/gfx/size.h
+++ b/ui/gfx/size.h
@@ -11,6 +11,7 @@
 #include "ui/base/ui_export.h"
 #include "ui/gfx/size_base.h"
 #include "ui/gfx/size_f.h"
+#include "ui/gfx/vector2d.h"
 
 #if defined(OS_WIN)
 typedef struct tagSIZE SIZE;
@@ -66,6 +67,10 @@ inline bool operator!=(const Size& lhs, const Size& rhs) {
   return !(lhs == rhs);
 }
 
+inline Size SizeOfVector2d(const Vector2d& v) {
+  return Size(std::abs(v.x()), std::abs(v.y()));
+}
+
 #if !defined(COMPILER_MSVC)
 extern template class SizeBase<Size, int>;
 #endif