Add a shadow to the FloatingActionButton.

sky/sdk/lib/framework/painting/shadows.dart

+// 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.
+
+import 'dart:sky' as sky;
+
+/// Helper class to build a Paint DrawLooper that adds shadows to the Paint's
+/// operation.
+class ShadowDrawLooperBuilder {
+  var builder_ = new sky.LayerDrawLooperBuilder();
+
+  void addShadow(sky.Size offset, sky.Color color, double blur) {
+    builder_.addLayerOnTop(
+          new sky.DrawLooperLayerInfo()
+            ..setPaintBits(-1)
+            ..setOffset(offset.toPoint())
+            ..setColorMode(sky.TransferMode.srcMode),
+          (sky.Paint layerPaint) {
+        layerPaint.color = color;
+        layerPaint.setMaskFilter(
+          new sky.MaskFilter.Blur(sky.BlurStyle.normal,
+                                  blur,
+                                  highQuality: true));
+      });
+  }
+
+  sky.DrawLooper build() {
+    builder_.addLayerOnTop(new sky.DrawLooperLayerInfo(), (_) {});
+    return builder_.build();
+  }
+}