Revert "Remove Expect from core library."

tests/corelib/core_runtime_types_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";
-
 /**
  * A test of simple runtime behavior on numbers, strings and lists with
  * a focus on both correct behavior and runtime errors.
  *
  * This file is written to use minimal type declarations to match a
  * typical dynamic language coding style.
  */
 class CoreRuntimeTypesTest {
   static testMain() {
     testBooleanOperators();
@@ skipping 259 matching lines @@
     '${true}'.toString();
     '${false}'.toString();
     ''.toString();
     ''.endsWith('');
   }
 }
 
 main() {
   CoreRuntimeTypesTest.testMain();
 }