Revert "Remove Expect from core library."

tests/standalone/double_temp_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 correct usage of inlined double temporary objects.
 
-import "package:expect/expect.dart";
-
 main() {
   for (int i = 0; i < 2000; i++) {
     testBinaryOp();
     testUnaryOp();
   }
 }
 
 
 // VM: temporary double should not be used as result of division,
 // otherwise the function always returns the same object.
@@ skipping 13 matching lines @@
 double unary(double a, double b) {
   return -(a * (-b));
 }
 
 
 testUnaryOp() {
   var x = unary(1.0, 2.0);
   var y = unary(3.0, 4.0);
   Expect.equals(2.0, x);
 }