Add Object.hashCodeOf to get the default hashCode of an object.

tests/corelib/hashcode_test.dart

Index: tests/corelib/hashcode_test.dart
diff --git a/tests/corelib/hashcode_test.dart b/tests/corelib/hashcode_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..41a272f6de8537253fe3567266edad68c0d5c474
--- /dev/null
+++ b/tests/corelib/hashcode_test.dart
@@ -0,0 +1,48 @@
+// Copyright (c) 2013, 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";
+
+class Override {
+  int hash;
+  int get superHash => super.hashCode;
+  int get hashCode => hash;
+
+  int foo() => hash;   // Just some function that can be closurized.
+
+  bool operator==(Object other) =>
+      other is Override && (other as Override).hash == hash;
+}
+
+int bar() => 42;  // Some global function.
+
+main() {
+  var o = new Object();
+  var hash = o.hashCode;
+  // Doesn't change.
+  Expect.equals(hash, o.hashCode);
+  Expect.equals(hash, identityHashCode(o));
+
+  var c = new Override();
+  int identityHash = c.superHash;
+  hash = (identityHash == 42) ? 37 : 42;
+  c.hash = hash;
+  Expect.equals(hash, c.hashCode);
+  Expect.equals(identityHash, identityHashCode(c));
+
+  // These classes don't override hashCode.
+  var samples = [0, 0x10000000, 1.5, -0, null, true, false, const Object()];
+  for (var v in samples) {
+    print(v);
+    Expect.equals(v.hashCode, identityHashCode(v));
+  }
+  // These do, or might do, but we can still use hashCodeOf and get the same
+  // result each time.
+  samples = ["string", "", (x) => 42, c.foo, bar];
+  for (var v in samples) {
+    print(v);
+    Expect.equals(v.hashCode, v.hashCode);
+    Expect.equals(identityHashCode(v), identityHashCode(v));
+  }
+}