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

tests/corelib/list_test.dart

Index: tests/corelib/list_test.dart
diff --git a/tests/corelib/list_test.dart b/tests/corelib/list_test.dart
index 8883e491aa5a401a888487feb0b15627052c6a85..deb26547a50d483c6711554e3f4eed6c788d1a4a 100644
--- a/tests/corelib/list_test.dart
+++ b/tests/corelib/list_test.dart
@@ -44,6 +44,8 @@ void main() {
   testTypedGrowableList(new Int16List(0).toList());
   testTypedGrowableList(new Uint32List(0).toList());
   testTypedGrowableList(new Int32List(0).toList());
+
+  testListConstructor();
 }
 
 void testLength(int length, List list) {
@@ -492,3 +494,13 @@ class MyFixedList<E> extends ListBase<E> {
   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.
+}