Revert "Remove Expect from core library."

tests/language/positional_parameters_type_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.
 // VMOptions=--enable_type_checks
 //
 // Dart test program for testing optional positional parameters in type tests.
 
-import "package:expect/expect.dart";
-
 class NamedParametersTypeTest {
   static int testMain() {
     int result = 0;
     Function anyFunction;
     void acceptFunNumOptBool(void funNumOptBool(num n, [bool b])) { };
     void funNum(num n) { };
     void funNumBool(num n, bool b) { };
     void funNumOptBool(num n, [bool b = true]) { };
     void funNumOptBoolX(num n, [bool x = true]) { };
     anyFunction = funNum;  // No error.
@@ skipping 20 matching lines @@
     } on TypeError catch (error) {
       result += 100;
     }
     return result;
   }
 }
 
 main() {
   Expect.equals(11, NamedParametersTypeTest.testMain());
 }