Add a simple dominator based redundancy elimination.

runtime/vm/hash_map_test.cc

 // 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.
 
 #include "platform/assert.h"
 #include "vm/unit_test.h"
 #include "vm/hash_map.h"
 
 namespace dart {
 
@@ skipping 12 matching lines @@
   EXPECT(map.IsEmpty());
   TestValue v1(0);
   TestValue v2(1);
   TestValue v3(0);
   map.Insert(&v1);
   EXPECT(map.Lookup(&v1) == &v1);
   map.Insert(&v2);
   EXPECT(map.Lookup(&v1) == &v1);
   EXPECT(map.Lookup(&v2) == &v2);
   EXPECT(map.Lookup(&v3) == &v1);
+  DirectChainedHashMap<TestValue*> map2(map);
+  EXPECT(map2.Lookup(&v1) == &v1);
+  EXPECT(map2.Lookup(&v2) == &v2);
+  EXPECT(map2.Lookup(&v3) == &v1);
 }
 
 }  // namespace dart