Update List constructor documentation. Say that null is not a length.

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 26 matching lines @@
   testGrowableList((const []).toList());
   testGrowableList(new MyList([]));
   testGrowableList(new MyList([]).toList());
 
   testTypedGrowableList(new Uint8List(0).toList());
   testTypedGrowableList(new Int8List(0).toList());
   testTypedGrowableList(new Uint16List(0).toList());
   testTypedGrowableList(new Int16List(0).toList());
   testTypedGrowableList(new Uint32List(0).toList());
   testTypedGrowableList(new Int32List(0).toList());
+
+  testListConstructor();
 }
 
 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
@@ skipping 428 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; }
 }
+
+void testListConstructor() {
+  Expect.throws(() { new List(0).add(4); });  // Is fixed-length.
+  Expect.throws(() { new List(-2); });  // Not negative.
+  Expect.throws(() { new List(null); });  // Not null.
+  Expect.listEquals([4], new List()..add(4));
+  Expect.throws(() { new List.filled(0, 42).add(4); });  // Is fixed-length.
+  Expect.throws(() { new List.filled(-2, 42); });  // Not negative.
+  Expect.throws(() { new List.filled(null, 42); });  // Not null.
+}