Add helpers library to dart2js.

sdk/lib/_internal/compiler/implementation/helpers/debug_collection.dart

+// Copyright (c) 2014, 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 dart2js.helpers;
+
+typedef void DebugCallback(String methodName, var arg1, var arg2);
+
+class DebugMap<K, V> implements Map<K, V> {
+  final Map<K, V> map;
+  DebugCallback indexSetCallBack;
+  DebugCallback putIfAbsentCallBack;
+
+  DebugMap(this.map, {DebugCallback addCallback}) {
+    if (addCallback != null) {
+      this.addCallback = addCallback;
+    }
+  }
+
+  void set addCallback(DebugCallback value) {
+    indexSetCallBack = value;
+    putIfAbsentCallBack = value;
+  }
+
+  bool containsValue(Object value) {
+    return map.containsValue(value);
+  }
+
+  bool containsKey(Object key) => map.containsKey(key);
+
+  V operator [](Object key) => map[key];
+
+  void operator []=(K key, V value) {
+    if (indexSetCallBack != null) {
+      indexSetCallBack('[]=', key, value);
+    }
+    map[key] = value;
+  }
+
+  V putIfAbsent(K key, V ifAbsent()) {
+    return map.putIfAbsent(key, () {
+     V v = ifAbsent();

[karlklose, 2014/03/25 14:22:18]

Indentation is off.

[Johnni Winther, 2014/03/26 07:35:05]

Done.

+     if (putIfAbsentCallBack != null) {
+       putIfAbsentCallBack('putIfAbsent', key, v);
+     }
+     return v;
+    });
+  }
+
+  void addAll(Map<K, V> other) => map.addAll(other);
+
+  V remove(Object key) => map.remove(key);
+
+  void clear() => map.clear();
+
+  void forEach(void f(K key, V value)) => map.forEach(f);
+
+  Iterable<K> get keys => map.keys;
+
+  Iterable<V> get values => map.values;
+
+  int get length => map.length;
+
+  bool get isEmpty => map.isEmpty;
+
+  bool get isNotEmpty => map.isNotEmpty;
+}