Revert "Remove Expect from core library."

tests/language/function_test.dart

 // Copyright (c) 2011, 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";
-
 // Tests function statements and expressions.
 
 class Bug4089219 {
   int x;
   var f;
 
   Bug4089219(int i) : this.x = i {
     f = () => x;
   }
 }
@@ skipping 286 matching lines @@
     fooIntString = foo;
 
     uf = uf2;
     uf2 = uf;
   }
 }
 
 main() {
   FunctionTest.testMain();
 }