Add a new implementation of HashMap that uses JS objects for its (multiple) hash tables.

runtime/lib/collection_patch.dart

Index: runtime/lib/collection_patch.dart
diff --git a/tests/compiler/dart2js_native/is_check_test.dart b/runtime/lib/collection_patch.dart
similarity index 69%
copy from tests/compiler/dart2js_native/is_check_test.dart
copy to runtime/lib/collection_patch.dart
index f0ae31152918cbaf39c6b3f5c54e8358b063c10e..062efc029067acdbf70adadcea567de76ef6d1c3 100644
--- a/tests/compiler/dart2js_native/is_check_test.dart
+++ b/runtime/lib/collection_patch.dart
@@ -2,9 +2,6 @@
 // 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.
 
-class A native "*A" {}
-

[erikcorry, 2013/03/22 12:59:24]

I think Rietveld is screwing with us here.

-main() {
-  var a = [new Object()];
-  Expect.isFalse(a[0] is A);
+patch class HashMap<K, V> {
+  /* patch */ factory HashMap() => new HashMap<K, V>._internal();
 }