Add a simple compositor for Sky

mojo/converters/geometry/geometry_type_converters.h

Index: mojo/converters/geometry/geometry_type_converters.h
diff --git a/mojo/converters/geometry/geometry_type_converters.h b/mojo/converters/geometry/geometry_type_converters.h
index 5d523746d65da51e9794adf5f1b3d602443a067c..bdb29e7dd4124ebaa223fb85231df03d1958185d 100644
--- a/mojo/converters/geometry/geometry_type_converters.h
+++ b/mojo/converters/geometry/geometry_type_converters.h
@@ -70,6 +70,15 @@ struct MOJO_GEOMETRY_EXPORT TypeConverter<gfx::Transform, TransformPtr> {
 };
 
 template <>
+struct MOJO_GEOMETRY_EXPORT TypeConverter<Size, gfx::Size> {
+  static Size Convert(const gfx::Size& input);
+};
+template <>
+struct MOJO_GEOMETRY_EXPORT TypeConverter<gfx::Size, Size> {
+  static gfx::Size Convert(const Size& input);
+};
+
+template <>
 struct MOJO_GEOMETRY_EXPORT TypeConverter<Rect, gfx::Rect> {
   static Rect Convert(const gfx::Rect& input);
 };