Change new List(n) to return fixed length list.

tests/corelib/list_removeat_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.
 
 void main() {
   // Normal modifiable list.
   var l1 = [0, 1, 2, 3, 4];
 
   bool checkedMode = false;
   assert(checkedMode = true);
@@ skipping 24 matching lines @@
   Expect.equals(4, l1[3], "l1-1[3]");
   Expect.equals(4, l1.length, "length-1");
 
   Expect.equals(0, l1.removeAt(0), "l1-remove0");
   Expect.equals(1, l1[0], "l1-2[0]");
   Expect.equals(3, l1[1], "l1-2[1]");
   Expect.equals(4, l1[2], "l1-2[2]");
   Expect.equals(3, l1.length, "length-2");
 
   // Fixed size list.
-  var l2 = new List.fixedLength(5);
+  var l2 = new List(5);
   for (var i = 0; i < 5; i++) l2[i] = i;
   Expect.throws(() { l2.removeAt(2); },
                 (e) => e is UnsupportedError,
                 "fixed-length");
 
   // Unmodifiable list.
   var l3 = const [0, 1, 2, 3, 4];
   Expect.throws(() { l3.removeAt(2); },
                 (e) => e is UnsupportedError,
                 "unmodifiable");
 
   // Empty list is not special.
   var l4 = [];
   Expect.throws(() { l4.removeAt(0); },
                 (e) => e is RangeError,
                 "empty");
 }