Revert "Remove Expect from core library."

tests/compiler/dart2js/find_my_name_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 "package:expect/expect.dart";
 import "../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart";
 import "mock_compiler.dart";
 import "parser_helper.dart";
 
 main() {
   MockCompiler compiler = new MockCompiler();
 
   String code = '''
 class Foo {
   operator+(other) => null;
 }
 ''';
 
   ClassElement foo = parseUnit(code, compiler, compiler.mainApp).head;
   foo.parseNode(compiler);
   for (Element e in foo.localMembers) {
     Expect.equals(code.indexOf(e.name.slowToString()), e.position().charOffset);
   }
 }