Use an enum for Dart bindings for Skia Paint style

sky/engine/core/painting/Paint.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
   Constructor(),
 ] interface Paint {
-  // Style
-  const unsigned short FILL_STYLE            = 0;
-  const unsigned short STROKE_STYLE          = 1;
-  const unsigned short STROKE_AND_FILL_STYLE = 2;
-
-  // TODO(jackson): we could wrap this enum like we did for |color|
-  attribute unsigned short style;
   attribute float strokeWidth;
   attribute boolean isAntiAlias;
   attribute Color color;
 
   // TODO(mpcomplete): remove this in favor of assigning to |color|.
   void setARGB(unsigned long a, unsigned long r, unsigned long g, unsigned long b);
   void setDrawLooper(DrawLooper looper);
   void setColorFilter(ColorFilter filter);
   void setMaskFilter(MaskFilter filter);
+  void setStyle(PaintingStyle style);
   void setTransferMode(TransferMode transferMode);
 };