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

"=>" breaks if the delegate wraps a subclass that adds a return
type (e.g. DelegatingSink wrapping a StreamSink).

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1242943010 .
diff --git a/lib/src/delegate/event_sink.dart b/lib/src/delegate/event_sink.dart
index 1fe86c1..337e7a8 100644
--- a/lib/src/delegate/event_sink.dart
+++ b/lib/src/delegate/event_sink.dart
@@ -16,10 +16,15 @@
   /// Create a delegating sink forwarding calls to [sink].
   DelegatingEventSink(EventSink 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);
+  }
 
-  void close() => _sink.close();
+  void close() {
+    _sink.close();
+  }
 }
diff --git a/lib/src/delegate/sink.dart b/lib/src/delegate/sink.dart
index 5cf4f56..bb50da3 100644
--- a/lib/src/delegate/sink.dart
+++ b/lib/src/delegate/sink.dart
@@ -15,7 +15,11 @@
   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();
+  }
 }
diff --git a/lib/src/delegate/stream_sink.dart b/lib/src/delegate/stream_sink.dart
index 9742b4c..b6ace65 100644
--- a/lib/src/delegate/stream_sink.dart
+++ b/lib/src/delegate/stream_sink.dart
@@ -19,10 +19,13 @@
   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);