Revert "Remove Expect from core library."

tests/language/try_catch5_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 {
       try {
         a = 8;
         return;
       } finally {
         b = 8 == a;
         entered = true;
         continue;
       }
     } finally {
       continue;
     }
   }
 }
 
 main() {
   a = 0;
   Expect.isTrue(foo1());
 }