Move minitest.dart into the expect package.

pkg/dev_compiler/test/codegen/lib/html/form_element_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.
 
 import 'dart:html';
 
-import 'package:minitest/minitest.dart';
+import 'package:expect/minitest.dart';
 
 void main() {
   var isFormElement = predicate((x) => x is FormElement, 'is a FormElement');
 
   test('constructorTest1', () {
     var form = new FormElement();
     expect(form, isNotNull);
     expect(form, isFormElement);
   });
 
@@ skipping 54 matching lines @@
     form.noValidate = true;
     expect(form.noValidate, true);
   });
 
   test('targetTest', () {
     var target = 'target';
     form.target = target;
     expect(form.target, target);
   });
 }