Revert "Remove Expect from core library."

tests/compiler/dart2js/analyze_all_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 'compiler_helper.dart';
 
 const String SOURCE = """
 class Foo {
   // Deliberately not const to ensure compile error.
   Foo(_);
 }
 
 @Bar()
 class Bar {
@@ skipping 26 matching lines @@
                 'expected exactly two errors, but got ${compiler.errors}');
 
   Expect.equals(MessageKind.CONSTRUCTOR_IS_NOT_CONST,
                 compiler.errors[0].message.kind);
   Expect.equals("Foo", compiler.errors[0].node.toString());
 
   Expect.equals(MessageKind.CONSTRUCTOR_IS_NOT_CONST,
                 compiler.errors[1].message.kind);
   Expect.equals("Foo", compiler.errors[1].node.toString());
 }