Make adding and subtracting gfx:: point types simpler.

ui/gfx/size.h

Index: ui/gfx/size.h
diff --git a/ui/gfx/size.h b/ui/gfx/size.h
index 2d01eeea5004f53893d214c3c3915b113ad84050..8a53b97edbcc6c55a0b6ac7bb7de18fdf9a39e56 100644
--- a/ui/gfx/size.h
+++ b/ui/gfx/size.h
@@ -10,6 +10,7 @@
 #include "build/build_config.h"
 #include "ui/base/ui_export.h"
 #include "ui/gfx/size_base.h"
+#include "ui/gfx/size_f.h"
 
 #if defined(OS_WIN)
 typedef struct tagSIZE SIZE;
@@ -42,6 +43,10 @@ class UI_EXPORT Size : public SizeBase<Size, int> {
   CGSize ToCGSize() const;
 #endif
 
+  SizeF ToSizeF() const {
+    return SizeF(width(), height());
+  }
+
   std::string ToString() const;
 };