Add TransferMode to dart:sky, and use it instead of passing ints around.

sky/engine/core/painting/ColorFilter.cpp

Index: sky/engine/core/painting/ColorFilter.cpp
diff --git a/sky/engine/core/painting/ColorFilter.cpp b/sky/engine/core/painting/ColorFilter.cpp
index 964fe3d57d4e3269cd992bd70067c8d1e38b2f89..819c4e89a6441288f3763258d52ae359d239dc48 100644
--- a/sky/engine/core/painting/ColorFilter.cpp
+++ b/sky/engine/core/painting/ColorFilter.cpp
@@ -8,11 +8,10 @@
 namespace blink {
 
 // static
-PassRefPtr<ColorFilter> ColorFilter::create(unsigned color,
-                                            unsigned transfer_mode) {
+PassRefPtr<ColorFilter> ColorFilter::create(CanvasColor color,
+                                            TransferMode transfer_mode) {
   return adoptRef(new ColorFilter(adoptRef(SkColorFilter::CreateModeFilter(
-      static_cast<SkColor>(color),
-      static_cast<SkXfermode::Mode>(transfer_mode)))));
+      color.sk_color, transfer_mode.sk_mode))));
 }
 
 ColorFilter::ColorFilter(PassRefPtr<SkColorFilter> filter)