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

tests/html/native_gc_test.dart

 library NativeGCTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 var testEvent = new EventStreamProvider<Event>('test');
 
 main() {
   useHtmlConfiguration();
 
   test('EventListener', () {
       final int N = 1000000;
       final int M = 1000;
 
       var div;
       for (int i = 0; i < M; ++i) {
         // This memory should be freed when the listener below is
         // collected.
-        List l = new List.fixedLength(N);
+        List l = new List(N);
 
         // Record the iteration number.
         l[N - 1] = i;
 
         div = new Element.tag('div');
         testEvent.forTarget(div).listen((_) {
             // Only the final iteration's listener should be invoked.
             // Note: the reference to l keeps the entire list alive.
             expect(l[N - 1], M - 1);
           });
@@ skipping 16 matching lines @@
     for (int i = 0; i < 100; ++i) {
       triggerMajorGC();
     }
 
     testDiv.onClick.listen(expectAsync1((e) {}));
     window.postMessage(message, '*');
   });
 }
 
 void triggerMajorGC() {
-  List list = new List.fixedLength(1000000);
+  List list = new List(1000000);
   Element div = new DivElement();
   div.onClick.listen((e) => print(list[0]));
 }