Revert "Remove Expect from core library."

tests/language/deopt_inlined_function_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 deoptimization from within an inlined function.
 
-import "package:expect/expect.dart";
-
 class A {
   deopt_here() => 1;
 }
 
 class B {
   deopt_here() => 2;
 }
 
 var obj = new A();
 
 bar(x) {
   x = 42;
   obj.deopt_here();
   return x;
 }
 
 foo(x) {
   x = bar(x);
   return x;
 }
 
 main() {
   Expect.equals(42, foo(1));
   for (var i = 0; i < 2000; i++) foo(7);
   Expect.equals(42, foo(2));
   obj = new B();
   Expect.equals(42, foo(3));  // <-- deoptimization via foo/bar/obj.deopt_here
 }