Adding isNotEmpty property to collection and string.

tests/corelib/list_test.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.
 
 import "dart:collection";
 import "dart:typed_data";
 import "package:expect/expect.dart";
 
 void main() {
   // Typed lists - fixed length and can only contain integers.
@@ skipping 31 matching lines @@
   testGrowableList(new Int8List(0).toList());
   testGrowableList(new Uint16List(0).toList());
   testGrowableList(new Int16List(0).toList());
   testGrowableList(new Uint32List(0).toList());
   testGrowableList(new Int32List(0).toList());
 }
 
 void testLength(int length, List list) {
   Expect.equals(length, list.length);
   (length == 0 ? Expect.isTrue : Expect.isFalse)(list.isEmpty);
+  (length != 0 ? Expect.isTrue : Expect.isFalse)(list.isNotEmpty);
 }
 
 void testTypedLengthInvariantOperations(List list) {
   // length
   Expect.equals(list.length, 4);
   // operators [], []=.
   for (int i = 0; i < 4; i++) list[i] = 0;
   list[0] = 4;
   Expect.listEquals([4, 0, 0, 0], list);
   list[1] = 7;
@@ skipping 407 matching lines @@
 }
 
 class MyFixedList<E> extends ListBase<E> {
   List<E> _source;
   MyFixedList(this._source);
   int get length => _source.length;
   void set length(int length) { throw new UnsupportedError("Fixed length!"); }
   E operator[](int index) => _source[index];
   void operator[]=(int index, E value) { _source[index] = value; }
 }