Adding isNotEmpty property to collection and string.

tools/dom/src/AttributeMap.dart

 // Copyright (c) 2012, 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 html;
 
 abstract class _AttributeMap implements Map<String, String> {
   final Element _element;
 
   _AttributeMap(this._element);
@@ skipping 52 matching lines @@
   }
 
   /**
    * Returns true if there is no {key, value} pair in the map.
    */
   bool get isEmpty {
     return length == 0;
   }
 
   /**
+   * Returns true if there is at least one {key, value} pair in the map.
+   */
+  bool get isNotEmpty => !isEmpty;
+
+  /**
    * Checks to see if the node should be included in this map.
    */
   bool _matches(Node node);
 }
 
 /**
  * Wrapper to expose [Element.attributes] as a typed map.
  */
 class _ElementAttributeMap extends _AttributeMap {
 
@@ skipping 126 matching lines @@
       }
     });
     return values;
   }
 
   int get length => keys.length;
 
   // TODO: Use lazy iterator when it is available on Map.
   bool get isEmpty => length == 0;
 
+  bool get isNotEmpty => !isEmpty;
+
   // Helpers.
   String _attr(String key) => 'data-$key';
   bool _matches(String key) => key.startsWith('data-');
   String _strip(String key) => key.substring(5);
 }