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

sky/engine/core/painting/MaskFilter.cpp

Index: sky/engine/core/painting/MaskFilter.cpp
diff --git a/sky/engine/core/painting/MaskFilter.cpp b/sky/engine/core/painting/MaskFilter.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..2bd1fafcb53b764e656d394a0fd9a3f61aef0355
--- /dev/null
+++ b/sky/engine/core/painting/MaskFilter.cpp
@@ -0,0 +1,26 @@
+// 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/MaskFilter.h"
+
+#include "third_party/skia/include/effects/SkBlurMaskFilter.h"
+
+namespace blink {
+
+// static
+PassRefPtr<MaskFilter> MaskFilter::create(
+      unsigned style, double sigma, unsigned flags) {
+  return adoptRef(new MaskFilter(adoptRef(SkBlurMaskFilter::Create(
+      static_cast<SkBlurStyle>(style), sigma, flags))));
+}
+
+MaskFilter::MaskFilter(PassRefPtr<SkMaskFilter> filter)
+    : filter_(filter) {
+}
+
+MaskFilter::~MaskFilter() {
+}
+
+} // namespace blink