Fix hash code tests to be non-flaky.

tests/compiler/dart2js_extra/hash_code_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";
 
 // dart2js specific test to make sure hashCode on intercepted types behaves as
 // intended.
 
 
 class Hasher {
   confuse(x) => [1, 'x', true, null, x].last;
   hash(x) => confuse(x).hashCode;
 }
 
 // Hashing via [hash] should be forced to use the general interceptor, but the
 // local x.hashCode calls might be optimized.
 var hash = new Hasher().hash;
 
-check(value1, value2) {
+check(value1, value2, {identityHashCode}) {

[ahe, 2013/06/04 13:19:49]

bool identityHashCode: false

   var h1 = hash(value1);
   var h2 = hash(value2);
-
   Expect.isTrue(h1 is int);
   Expect.isTrue(h2 is int);
-  Expect.isFalse(h1 == h2);
-
-  // We expect that the hash function is reasonable quality - there are some
-  // difference in the low bits.
-  Expect.isFalse((h1 & 0xf) == (h2 & 0xf));
 
   // Quality check - the values should be SMIs for efficient arithmetic.
   Expect.equals((h1 & 0x3fffffff), h1);
   Expect.equals((h2 & 0x3fffffff), h2);
+
+  // If we're checking the (randomized) identity hash code function,
+  // we cannot guarantee anything about the actual hash code values.
+  if (identityHashCode) return;

[ahe, 2013/06/04 13:19:49]

Otherwise this will fail in checked mode.

+
+  // We expect that the hash function is reasonable quality - there
+  // are some difference in the low bits.
+  Expect.isFalse(h1 == h2);
+  Expect.isFalse((h1 & 0xf) == (h2 & 0xf));
 }
 
 bools() {
-  check(true, false);
+  check(true, false, identityHashCode: false);
 
   Expect.equals(true.hashCode, hash(true));   // First can be optimized.
   Expect.equals(false.hashCode, hash(false));
 }
 
 ints() {
   var i1 = 100;
   var i2 = 101;
-  check(i1, i2);
+  check(i1, i2, identityHashCode: false);
   Expect.equals(i1.hashCode, hash(i1));
   Expect.equals(i2.hashCode, hash(i2));
 }
 
 lists() {
   var list1 = [];
   var list2 = [];
-  check(list1, list2);
+  check(list1, list2, identityHashCode: true);
 
   Expect.equals(list1.hashCode, hash(list1));
   Expect.equals(list2.hashCode, hash(list2));
 }
 
 strings() {
   var str1 = 'a';
   var str2 = 'b';
   var str3 = 'c';
-  check(str1, str2);
-  check(str1, str3);
-  check(str2, str3);
+  check(str1, str2, identityHashCode: false);
+  check(str1, str3, identityHashCode: false);
+  check(str2, str3, identityHashCode: false);
 
   Expect.equals(str1.hashCode, hash(str1));
   Expect.equals(str2.hashCode, hash(str2));
   Expect.equals(str3.hashCode, hash(str3));
 
   Expect.equals(0xA2E9442, 'a'.hashCode);
   Expect.equals(0x0DB819B, 'b'.hashCode);
   Expect.equals(0xEBA5D59, 'c'.hashCode);
 }
 
 main() {
   bools();
   ints();
   lists();
   strings();
 }