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

runtime/lib/collection_patch.dart

 // 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.
 
-part of dart.collection;
+patch class HashMap<K, V> {
+  final _HashMapTable<K, V> _hashTable = new _HashMapTable<K, V>();
 
-class _HashMapTable<K, V> extends _HashTable<K> {
-  static const int _INITIAL_CAPACITY = 8;
-  static const int _VALUE_INDEX = 1;
-
-  _HashMapTable() : super(_INITIAL_CAPACITY);
-
-  int get _entrySize => 2;
-
-  V _value(int offset) => _table[offset + _VALUE_INDEX];
-  void _setValue(int offset, V value) { _table[offset + _VALUE_INDEX] = value; }
-
-  _copyEntry(List fromTable, int fromOffset, int toOffset) {
-    _table[toOffset + _VALUE_INDEX] = fromTable[fromOffset + _VALUE_INDEX];
-  }
-}
-
-class HashMap<K, V> implements Map<K, V> {
-  final _HashMapTable<K, V> _hashTable;
-
-  HashMap() : _hashTable = new _HashMapTable<K, V>() {
+  /* patch */ HashMap() {
     _hashTable._container = this;
   }
 
-  factory HashMap.from(Map<K, V> other) {
-    return new HashMap<K, V>()..addAll(other);
-  }
 
-  bool containsKey(K key) {
+  /* patch */ bool containsKey(K key) {
     return _hashTable._get(key) >= 0;
   }
 
-  bool containsValue(V value) {
+  /* patch */ bool containsValue(V value) {
     List table = _hashTable._table;
     int entrySize = _hashTable._entrySize;
     for (int offset = 0; offset < table.length; offset += entrySize) {
       if (!_hashTable._isFree(table[offset]) &&
           _hashTable._value(offset) == value) {
         return true;
       }
     }
     return false;
   }
 
-  void addAll(Map<K, V> other) {
+  /* patch */ void addAll(Map<K, V> other) {
     other.forEach((K key, V value) {
       int offset = _hashTable._put(key);
       _hashTable._setValue(offset, value);
       _hashTable._checkCapacity();
     });
   }
 
-  V operator [](K key) {
+  /* patch */ V operator [](K key) {
     int offset = _hashTable._get(key);
     if (offset >= 0) return _hashTable._value(offset);
     return null;
   }
 
-  void operator []=(K key, V value) {
+  /* patch */ void operator []=(K key, V value) {
     int offset = _hashTable._put(key);
     _hashTable._setValue(offset, value);
     _hashTable._checkCapacity();
   }
 
-  V putIfAbsent(K key, V ifAbsent()) {
+  /* patch */ V putIfAbsent(K key, V ifAbsent()) {
     int offset = _hashTable._probeForAdd(_hashTable._hashCodeOf(key), key);
     Object entry = _hashTable._table[offset];
     if (!_hashTable._isFree(entry)) {
       return _hashTable._value(offset);
     }
     int modificationCount = _hashTable._modificationCount;
     V value = ifAbsent();
     if (modificationCount == _hashTable._modificationCount) {
       _hashTable._setKey(offset, key);
       _hashTable._setValue(offset, value);
       if (entry == null) {
         _hashTable._entryCount++;
         _hashTable._checkCapacity();
       } else {
         assert(identical(entry, _TOMBSTONE));
         _hashTable._deletedCount--;
       }
       _hashTable._recordModification();
     } else {
       // The table might have changed, so we can't trust [offset] any more.
       // Do another lookup before setting the value.
       offset = _hashTable._put(key);
       _hashTable._setValue(offset, value);
       _hashTable._checkCapacity();
     }
     return value;
   }
 
-  V remove(K key) {
+  /* patch */ V remove(K key) {
     int offset = _hashTable._remove(key);
     if (offset < 0) return null;
     V oldValue = _hashTable._value(offset);
     _hashTable._setValue(offset, null);
     _hashTable._checkCapacity();
     return oldValue;
   }
 
-  void clear() {
+  /* patch */ void clear() {
     _hashTable._clear();
   }
 
-  void forEach(void action (K key, V value)) {
+  /* patch */ void forEach(void action(K key, V value)) {
     int modificationCount = _hashTable._modificationCount;
     List table = _hashTable._table;
     int entrySize = _hashTable._entrySize;
     for (int offset = 0; offset < table.length; offset += entrySize) {
       Object entry = table[offset];
       if (!_hashTable._isFree(entry)) {
         K key = entry;
         V value = _hashTable._value(offset);
         action(key, value);
         _hashTable._checkModification(modificationCount);
       }
     }
   }
 
-  Iterable<K> get keys => new _HashTableKeyIterable<K>(_hashTable);
-  Iterable<V> get values =>
+  /* patch */ Iterable<K> get keys => new _HashTableKeyIterable<K>(_hashTable);
+  /* patch */ Iterable<V> get values =>
       new _HashTableValueIterable<V>(_hashTable, _HashMapTable._VALUE_INDEX);
 
-  int get length => _hashTable._elementCount;
+  /* patch */ int get length => _hashTable._elementCount;
 
-  bool get isEmpty => _hashTable._elementCount == 0;
-
-  String toString() => Maps.mapToString(this);
+  /* patch */ bool get isEmpty => _hashTable._elementCount == 0;
 }