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/sdk/lib/collection/hash_map.dart b/runtime/lib/collection_patch.dart
similarity index 68%
copy from sdk/lib/collection/hash_map.dart
copy to runtime/lib/collection_patch.dart
index d90b4b9f0646c5ebbb689695696bf87f07a94d51..a9b74b7b4dc33b13cd702f65bbf547b8171f66df 100644
--- a/sdk/lib/collection/hash_map.dart
+++ b/runtime/lib/collection_patch.dart
@@ -2,40 +2,19 @@
 // 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) {
@@ -47,7 +26,7 @@ class HashMap<K, V> implements Map<K, V> {
     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);
@@ -55,19 +34,19 @@ class HashMap<K, V> implements Map<K, V> {
     });
   }
 
-  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)) {
@@ -96,7 +75,7 @@ class HashMap<K, V> implements Map<K, V> {
     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);
@@ -105,11 +84,11 @@ class HashMap<K, V> implements Map<K, V> {
     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;
@@ -124,13 +103,11 @@ class HashMap<K, V> implements Map<K, V> {
     }
   }
 
-  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;
-
-  bool get isEmpty => _hashTable._elementCount == 0;
+  /* patch */ int get length => _hashTable._elementCount;
 
-  String toString() => Maps.mapToString(this);
+  /* patch */ bool get isEmpty => _hashTable._elementCount == 0;
 }