Revert "Remove Expect from core library."

tests/language/char_escape_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.
 // Dart test for reading escape sequences in string literals
 
-import "package:expect/expect.dart";
-
 class CharEscapeTest {
   static testMain() {
     var x00 = "\x00";
     var u0000 = "\u0000";
     var v0 = "\u{0}";
     var v00 = "\u{00}";
     var v000 = "\u{000}";
     var v0000 = "\u{0000}";
     var v00000 = "\u{00000}";
     var v000000 = "\u{000000}";
@@ skipping 506 matching lines @@
     Expect.equals("\W", "W");
     Expect.equals("\X", "X");
     Expect.equals("\Y", "Y");
     Expect.equals("\Z", "Z");
   }
 }
 
 main() {
   CharEscapeTest.testMain();
 }