Move minitest.dart into the expect package.

pkg/dev_compiler/test/codegen/lib/html/geolocation_test.dart

  // Copyright (c) 2013, 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:html';
 
-import 'package:minitest/minitest.dart';
+import 'package:expect/minitest.dart';
 
 main() {
   // Actual tests require browser interaction. This just makes sure the API
   // is present.
   test('is not null', () {
     expect(window.navigator.geolocation, isNotNull);
   });
 }