fix unsound cast failures in tests

tests/corelib_strong/list_insert_all_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.
 
 import "package:expect/expect.dart";
 import "dart:collection";
 
-test(List list, int index, Iterable iterable) {
+test(List<int> list, int index, Iterable<int> iterable) {
   List copy = list.toList();
   list.insertAll(index, iterable);
   List iterableList = iterable.toList();
   Expect.equals(copy.length + iterableList.length, list.length);
   for (int i = 0; i < index; i++) {
     Expect.equals(copy[i], list[i]);
   }
   for (int i = 0; i < iterableList.length; i++) {
     Expect.equals(iterableList[i], list[i + index]);
   }
   for (int i = index + iterableList.length; i < copy.length; i++) {
     Expect.equals(copy[i], list[i + iterableList.length]);
   }
 }
 
-class MyList extends ListBase {
-  List list;
+class MyList<T> extends ListBase<T> {
+  List<T> list;
   MyList(this.list);
   get length => list.length;
   set length(value) {
     list.length = value;
   }
 
   operator [](index) => list[index];
   operator []=(index, val) {
     list[index] = val;
   }
@@ skipping 45 matching lines @@
   expectUE(() => test([1, 2, 3].toList(growable: false), 0, [4, 5]));
 }
 
 void expectRE(void f()) {
   Expect.throws(f, (e) => e is RangeError);
 }
 
 void expectUE(void f()) {
   Expect.throws(f, (e) => e is UnsupportedError);
 }