Revert "Remove Expect from core library."

tests/language/bailout2_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";
-
 var a;
 
 main() {
   // Write a loop to force a bailout method on [A.foo].
   for (int i = 0; i < 10; i++) {
     if (a != null) new A().foo([]);
     Expect.equals(42, new A().foo(new A()));
   }
 }
 
 class A {
   // In dart2js, the optimized version of foo tries to optimize the
   // uses of a.length (which is used two times here: for the index,
   // and for the bounds check), and that optmization used to crash
   // the compiler.
   foo(a) => a[a.length];
 
   int get length => 42;
   operator[] (index) => 42;
 }