Revert "Remove Expect from core library."

tests/language/try_catch4_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.
 // Check that our SSA graph does have the try body a predecessor of a
 // try/finally.
 
-import "package:expect/expect.dart";
-
 var a;
 
 foo1() {
   var b = false;
   var entered = false;
   while (true) {
     if (entered) return b;
     b = 8 == a; // This expression should not be GVN'ed.
     try {
       a = 8;
@@ skipping 169 matching lines @@
   Expect.isTrue(foo5());
   a = 0;
   Expect.isTrue(foo6());
   a = 0;
   Expect.isTrue(foo7());
   a = 0;
   Expect.isTrue(foo8());
   a = 0;
   Expect.isTrue(foo9());
 }