Make the HTTP MockClient work with GET requests.

pkg/http/test/mock_client_test.dart

 // Copyright (c) 2012, 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 mock_client_test;
 
 import 'dart:io';
 import 'dart:json';
 import 'dart:uri';
 
@@ skipping 36 matching lines @@
     });
 
     var uri = new Uri.fromString("http://example.com/foo");
     var request = new http.Request("POST", uri);
     request.body = "hello, world";
     var future = client.send(request)
         .chain(http.Response.fromStream)
         .transform((response) => response.body);
     expect(future, completion(equals('Request body was "hello, world"')));
   });
+
+  test('handles a request with no body', () {
+    var client = new MockClient((request) {
+      return new Future.immediate(new http.Response('you did it', 200));
+    });
+
+    expect(client.read("http://example.com/foo"),
+        completion(equals('you did it')));
+  });
 }