Revert "Remove Expect from core library."

tests/language/scoped_variables_try_catch_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 try/catch does not shadow a variable at runtime.
 
 main() {
   var a = bar();
   try {
     a = bar();
   } catch (e) {
   }
   Expect.equals(42, a);
 
   {
     var a = foo();
     try {
       a = foo();
     } catch (e) {
     }
     Expect.equals(54, a);
   }
 
   Expect.equals(42, a);
 }
 
 bar() => 42;
 foo() => 54;