Don't use "=>" for void methods in delegates.

lib/src/delegate/sink.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library async.delegate.sink;
 
 /// Simple delegating wrapper around a [Sink].
 ///
 /// Subclasses can override individual methods, or use this to expose only the
 /// [Sink] methods of a subclass.
 class DelegatingSink<T> implements Sink<T> {
   final Sink _sink;
 
   /// Create a delegating sink forwarding calls to [sink].
   DelegatingSink(Sink sink)
       : _sink = sink;
 
-  void add(T data) => _sink.add(data);
+  void add(T data) {
+    _sink.add(data);
+  }
 
-  void close() => _sink.close();
+  void close() {
+    _sink.close();
+  }
 }