Add an API to set the ColorFilter on a Paint object.

sky/engine/core/painting/Paint.h

Index: sky/engine/core/painting/Paint.h
diff --git a/sky/engine/core/painting/Paint.h b/sky/engine/core/painting/Paint.h
index d547474f6066fce99563c2da23f840bf7ebd1016..ed94297790d476748123eff48c3f24dd331d9f42 100644
--- a/sky/engine/core/painting/Paint.h
+++ b/sky/engine/core/painting/Paint.h
@@ -13,6 +13,7 @@
 namespace blink {
 
 class DrawLooper;
+class ColorFilter;
 
 class Paint : public RefCounted<Paint>, public DartWrappable {
     DEFINE_WRAPPERTYPEINFO();
@@ -34,6 +35,7 @@ public:
         m_paint.setARGB(a, r, g, b);
     }
     void setDrawLooper(DrawLooper* looper);
+    void setColorFilter(ColorFilter* filter);
 
     const SkPaint& paint() const { return m_paint; }
     void setPaint(const SkPaint& paint) { m_paint = paint; }