Adds support for transfer mode in Paint and SpriteNode classes

sky/engine/core/painting/Paint.cpp

 // 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.
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/painting/Paint.h"
 
 #include "sky/engine/core/painting/ColorFilter.h"
 #include "sky/engine/core/painting/DrawLooper.h"
 #include "sky/engine/core/painting/MaskFilter.h"
@@ skipping 19 matching lines @@
     ASSERT(filter);
     m_paint.setColorFilter(filter->filter());
 }
 
 void Paint::setMaskFilter(MaskFilter* filter)
 {
     ASSERT(filter);
     m_paint.setMaskFilter(filter->filter());
 }
 
+void Paint::setTransferMode(SkXfermode::Mode transfer_mode)
+{
+    m_paint.setXfermodeMode(transfer_mode);
+}
+
 } // namespace blink