Fix strong mode warnings.

test/pool_test.dart

 // Copyright (c) 2014, 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.
 
 import 'dart:async';
 
 import 'package:fake_async/fake_async.dart';
 import 'package:pool/pool.dart';
 import 'package:stack_trace/stack_trace.dart';
 import 'package:test/test.dart';
@@ skipping 258 matching lines @@
       });
 
       pool.request();
     });
   });
 
   group("close()", () {
     test("disallows request() and withResource()", () {
       var pool = new Pool(1)..close();
       expect(pool.request, throwsStateError);
-      expect(() => pool.withResource(() {}), throwsStateError);
+      expect(pool.withResource(() {}), throwsStateError);
     });
 
     test("pending requests are fulfilled", () async {
       var pool = new Pool(1);
       var resource1 = await pool.request();
       expect(pool.request().then((resource2) {
         resource2.release();
       }), completes);
       expect(pool.close(), completes);
       resource1.release();
@@ skipping 129 matching lines @@
 ///
 /// This should only be called within a [FakeAsync.run] zone.
 Matcher get doesNotComplete => predicate((future) {
   expect(future, new isInstanceOf<Future>());
 
   var stack = new Trace.current(1);
   future.then((_) => registerException(
       new TestFailure("Expected future not to complete."), stack));
   return true;
 });