Revert "Remove Expect from core library."

tests/language/inline_value_context_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.
 // Test inlining of simple function with control flow in a value context.
 // Optimize function foo with instance of A and inlined function bar. Call later
 // with instance of B and cause deoptimization.
 
-import "package:expect/expect.dart";
-
 class A {
   var x = 1;
 }
 
 class B {
   var x = 0;
 }
 
 int bar(o) {
   if (o.x > 0) {  // <-- Deoptimize from inner frame.
@@ skipping 12 matching lines @@
 }
 
 main() {
   var o = new A();
   int sum = 0;
   for (int i = 0; i < 5000; i++) sum += foo(o);
   o = new B();
   sum += foo(o);  // <-- Cause deoptimization of bar within foo.
   Expect.equals(5000, sum);
 }