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

sdk/lib/collection/hash_map.dart

Index: sdk/lib/collection/hash_map.dart
diff --git a/sdk/lib/collection/hash_map.dart b/sdk/lib/collection/hash_map.dart
index d90b4b9f0646c5ebbb689695696bf87f07a94d51..676c89268e91e0a102f397c718a658ef6d2e1eef 100644
--- a/sdk/lib/collection/hash_map.dart
+++ b/sdk/lib/collection/hash_map.dart
@@ -21,16 +21,18 @@ class _HashMapTable<K, V> extends _HashTable<K> {
 }
 
 class HashMap<K, V> implements Map<K, V> {
-  final _HashMapTable<K, V> _hashTable;
+  final _HashMapTable<K, V> _hashTable = new _HashMapTable<K, V>();
 
-  HashMap() : _hashTable = new _HashMapTable<K, V>() {
-    _hashTable._container = this;
-  }
+  external factory HashMap();

[Ivan Posva, 2013/03/22 16:32:47]

Why stop here? There are plenty of other opportunities below. The way it is
structured even after your half-way ripping it apart is that you need to have
this internal _hashTable object even if you did not really need it.

[kasperl, 2013/03/22 16:36:01]

I need to have this _internal hashTable object even when I don't really need it?
I don't understand that?

 
   factory HashMap.from(Map<K, V> other) {
     return new HashMap<K, V>()..addAll(other);
   }
 
+  HashMap._internal() {
+    _hashTable._container = this;
+  }
+
   bool containsKey(K key) {
     return _hashTable._get(key) >= 0;
   }