Revert "Remove Expect from core library."

tests/language/type_error_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";
-
 // Test that various type errors doesn't invoke user-defined code
 // during error reporting.
 
 class MyClass {}
 
 class IntTypeError {
   toString() {
     int value = wrap(this);
     return super.toString();
   }
@@ skipping 170 matching lines @@
 
   checkCastError(new IntCastError());
   checkCastError(new StringCastError());
   checkCastError(new DoubleCastError());
   checkCastError(new NumCastError());
   checkCastError(new BoolCastError());
   checkCastError(new FunctionCastError());
   checkCastError(new MyClassCastError());
   checkCastError(new ListCastError());
 }