Fix one final strong-mode warning.

R=alanknight@google.com

Review URL: https://codereview.chromium.org//1944603004 .
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 82ea2c1..13a628a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
+## 0.11.3+6
+
+* Fix one more strong mode warning in `http/testing.dart`.
+
 ## 0.11.3+5
 
-* Fix some lingering strong mode warnings
+* Fix some lingering strong mode warnings.
 
 ## 0.11.3+4
 
diff --git a/lib/src/mock_client.dart b/lib/src/mock_client.dart
index 6bddbad..acda5fd 100644
--- a/lib/src/mock_client.dart
+++ b/lib/src/mock_client.dart
@@ -10,7 +10,6 @@
 import 'request.dart';
 import 'response.dart';
 import 'streamed_response.dart';
-import 'utils.dart';
 
 // TODO(nweiz): once Dart has some sort of Rack- or WSGI-like standard for
 // server APIs, MockClient should conform to it.
@@ -71,9 +70,9 @@
     });
 
   /// Sends a request.
-  Future<StreamedResponse> send(BaseRequest request) {
+  Future<StreamedResponse> send(BaseRequest request) async {
     var bodyStream = request.finalize();
-    return async.then((_) => _handler(request, bodyStream));
+    return await _handler(request, bodyStream);
   }
 }
 
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index a0f5e36..86a6690 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -117,9 +117,6 @@
   return completer.future;
 }
 
-/// Returns a [Future] that asynchronously completes to `null`.
-Future get async => new Future.value();
-
 /// A pair of values.
 class Pair<E, F> {
   E first;
diff --git a/pubspec.yaml b/pubspec.yaml
index 5e4b2c5..574cf00 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: http
-version: 0.11.3+5
+version: 0.11.3+6
 author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/http
 description: A composable, Future-based API for making HTTP requests.