Add a basic custom painting facility to Sky

sky/engine/core/painting/PaintingCallback.cpp

Index: sky/engine/core/painting/PaintingCallback.cpp
diff --git a/sky/engine/core/painting/Paint.cpp b/sky/engine/core/painting/PaintingCallback.cpp
similarity index 72%
copy from sky/engine/core/painting/Paint.cpp
copy to sky/engine/core/painting/PaintingCallback.cpp
index f3e6fcae0fbd241cca373bde147ae83dce270c6c..ef8da9ac85d916be2fb7b49fb54042a32ba12f89 100644
--- a/sky/engine/core/painting/Paint.cpp
+++ b/sky/engine/core/painting/PaintingCallback.cpp
@@ -3,15 +3,11 @@
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
-#include "sky/engine/core/painting/Paint.h"
+#include "sky/engine/core/painting/PaintingCallback.h"
 
 namespace blink {
 
-Paint::Paint()
-{
-}
-
-Paint::~Paint()
+PaintingCallback::~PaintingCallback()
 {
 }