Revert "Remove Expect from core library."

tests/language/type_variable_initializer_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 "package:expect/expect.dart";
-
 // Regression test for dart2js where the reference to [:this:] in a
 // constructor was not propagated to the super initializers.
 
 class A<T> {
   var map;
   // Usage of type variables in the intializer makes the SSA builder
   // want to access [:this:]. And because the initializers of A are
   // inlined in the constructor of B, we have to make sure the
   // [:this:] in the A constructor has a corresponding
   // SSA instruction.
   A() : map = new Map<T, T>();
 }
 
 class B<T> extends A<T> {
 }
 
 main() {
   Expect.isTrue(new B<int>().map is Map<int, int>);
 }