Revert "Remove Expect from core library."

tests/language/call_nonexistent_constructor_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";
-
 // When attempting to call a nonexistent constructor, check that a
 // NoSuchMethodError is thrown.
 
 foo() {
   throw 'hest';
 }
 
 class A {
   A.foo(var x) {}
 }
 
 main() {
   int i = 0;
   new A.foo(42);
   try {
     new A.bar(foo());  // Arguments are not evaluated with NoSuchMethodError.
   } on NoSuchMethodError catch (e) {  // Not 'on String catch ...'
     i = 1;
   }
   Expect.equals(1, i);
   try {
     new A();
   } on NoSuchMethodError catch (e) {
     i = 2;
   }
   Expect.equals(2, i);
 }