Add a MaskFilter interface to dart:sky to handle blur.

sky/engine/core/painting/MaskFilter.h

Index: sky/engine/core/painting/MaskFilter.h
diff --git a/sky/engine/core/painting/MaskFilter.h b/sky/engine/core/painting/MaskFilter.h
new file mode 100644
index 0000000000000000000000000000000000000000..e962397ac6c17c289abfd3ac7a3376e09fabd3dd
--- /dev/null
+++ b/sky/engine/core/painting/MaskFilter.h
@@ -0,0 +1,33 @@
+// 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.
+
+#ifndef SKY_ENGINE_CORE_PAINTING_MASKFILTER_H_
+#define SKY_ENGINE_CORE_PAINTING_MASKFILTER_H_
+
+#include "sky/engine/tonic/dart_wrappable.h"
+#include "sky/engine/wtf/PassRefPtr.h"
+#include "sky/engine/wtf/RefCounted.h"
+
+class SkMaskFilter;
+
+namespace blink {
+
+class MaskFilter : public RefCounted<MaskFilter>, public DartWrappable {
+  DEFINE_WRAPPERTYPEINFO();
+ public:
+  ~MaskFilter() override;
+  static PassRefPtr<MaskFilter> create(
+      unsigned style, double sigma, unsigned flags);
+
+  SkMaskFilter* filter() { return filter_.get(); }
+
+ private:
+  MaskFilter(PassRefPtr<SkMaskFilter> filter);
+
+  RefPtr<SkMaskFilter> filter_;
+};
+
+} // namespace blink
+
+#endif  // SKY_ENGINE_CORE_PAINTING_MASKFILTER_H_