Remove stale files from lib/html/src.

lib/html/src/DataAttributeMap.dart

-// Copyright (c) 2011, 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.
-
-/**
- * Provides a Map abstraction on top of data-* attributes, similar to the
- * dataSet in the old DOM.
- */
-class _DataAttributeMap implements AttributeMap {
-
-  final Map<String, String> _attributes;
-
-  _DataAttributeMap(this._attributes);
-
-  // interface Map
-
-  // TODO: Use lazy iterator when it is available on Map.
-  bool containsValue(String value) => getValues().some((v) => v == value);
-
-  bool containsKey(String key) => _attributes.containsKey(_attr(key));
-
-  String operator [](String key) => _attributes[_attr(key)];
-
-  void operator []=(String key, value) {
-    _attributes[_attr(key)] = '$value';
-  }
-
-  String putIfAbsent(String key, String ifAbsent()) {
-    if (!containsKey(key)) {
-      return this[key] = ifAbsent();
-    }
-    return this[key];
-  }
-
-  String remove(String key) => _attributes.remove(_attr(key));
-
-  void clear() {
-    // Needs to operate on a snapshot since we are mutatiting the collection.
-    for (String key in getKeys()) {
-      remove(key);
-    }
-  }
-
-  void forEach(void f(String key, String value)) {
-    _attributes.forEach((String key, String value) {
-      if (_matches(key)) {
-        f(_strip(key), value);
-      }
-    });
-  }
-
-  Collection<String> getKeys() {
-    final keys = new List<String>();
-    _attributes.forEach((String key, String value) {
-      if (_matches(key)) {
-        keys.add(_strip(key));
-      }
-    });
-    return keys;
-  }
-
-  Collection<String> getValues() {
-    final values = new List<String>();
-    _attributes.forEach((String key, String value) {
-      if (_matches(key)) {
-        values.add(value);
-      }
-    });
-    return values;
-  }
-
-  int get length() => getKeys().length;
-
-  // TODO: Use lazy iterator when it is available on Map.
-  bool isEmpty() => length == 0;
-
-  // Helpers.
-  String _attr(String key) => 'data-$key';
-  bool _matches(String key) => key.startsWith('data-');
-  String _strip(String key) => key.substring(5);
-}
-