Migrate test block 3 to Dart 2.0.

tests/corelib/collection_length_test.dart

-// Copyright (c) 2013, 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.
-
-library map_test;
-
-import 'dart:collection';
-
-// Test that length/isEmpty opertions are constant time on
-// maps, strings and collections.
-
-void testString(int n) {
-  String s = "x";
-  String string = "";
-  int length = n;
-  while (true) {
-    if ((length & 1) == 1) {
-      string += s;
-    }
-    length >>= 1;
-    if (length == 0) break;
-    s += s;
-  }
-  testLength(string, n);
-  testLength(string.codeUnits, n);
-}
-
-void testMap(Map map, int n) {
-  for (int i = 0; i < n; i++) {
-    map[i] = i;
-  }
-  testLength(map, n);
-  testLength(map.keys, n);
-  testLength(map.values, n);
-}
-
-void testCollection(var collection, n) {
-  for (int i = 0; i < n; i++) {
-    collection.add(i);
-  }
-  testLength(collection, n);
-}
-
-void testList(List list, n) {
-  // Works even if list is fixed-length.
-  for (int i = 0; i < n; i++) {
-    list[i] = i;
-  }
-  testLength(list, n);
-}
-
-void testLength(var lengthable, int size) {
-  print(lengthable.runtimeType); // Show what hangs the test.
-  int length = 0;
-  // If length, isEmpty or isNotEmpty is not a constant-time (or very fast)
-  // operation, this will timeout.
-  for (int i = 0; i < 100000; i++) {
-    if (!lengthable.isEmpty) length += lengthable.length;
-    if (lengthable.isNotEmpty) length += lengthable.length;
-  }
-  if (length != size * 200000) throw "Bad length: $length / size: $size";
-}
-
-main() {
-  const int N = 100000;
-  testMap(new HashMap(), N);
-  testMap(new LinkedHashMap(), N);
-  testMap(new SplayTreeMap(), N);
-  testCollection(new HashSet(), N);
-  testCollection(new LinkedHashSet(), N);
-  testCollection(new ListQueue(), N);
-  testCollection(new DoubleLinkedQueue(), N);
-  testList(new List()..length = N, N);
-  testList(new List(N), N);
-  testString(N);
-}