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

lib/src/delegate/stream_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.stream_sink;
 
 import 'dart:async';
 
 /// Simple delegating wrapper around a [StreamSink].
 ///
 /// Subclasses can override individual methods, or use this to expose only the
 /// [StreamSink] methods of a subclass.
 class DelegatingStreamSink<T> implements StreamSink<T> {
   final StreamSink _sink;
 
   Future get done => _sink.done;
 
   /// Create delegating sink forwarding calls to [sink].
   DelegatingStreamSink(StreamSink sink)
       : _sink = sink;
 
-  void add(T data) => _sink.add(data);
+  void add(T data) {
+    _sink.add(data);
+  }
 
-  void addError(error, [StackTrace stackTrace]) =>
-      _sink.addError(error, stackTrace);
+  void addError(error, [StackTrace stackTrace]) {
+    _sink.addError(error, stackTrace);
+  }
 
   Future addStream(Stream<T> stream) => _sink.addStream(stream);
 
   Future close() => _sink.close();
 }