fix unsound cast failures in tests

tests/corelib_strong/iterable_join_test.dart

Index: tests/corelib_strong/iterable_join_test.dart
diff --git a/tests/corelib_strong/iterable_join_test.dart b/tests/corelib_strong/iterable_join_test.dart
index e4f2f44afeec82baf8808ce196ce7b7da253339c..d9f325abf70f67ff7a57d90794359806586d7cdb 100644
--- a/tests/corelib_strong/iterable_join_test.dart
+++ b/tests/corelib_strong/iterable_join_test.dart
@@ -51,7 +51,7 @@ testCollections() {
   var setString = set.join();
   Expect.isTrue(perm.contains(setString), "set: $setString");
 
-  void testArray(array) {
+  void testArray(List<int> array) {
     testJoin("1,3,5,7,9", array.where((i) => i.isOdd), ",");
     testJoin("0,2,4,6,8,10,12,14,16,18", array.map((i) => i * 2), ",");
     testJoin("5,6,7,8,9", array.skip(5), ",");
@@ -61,7 +61,7 @@ testCollections() {
   }
 
   testArray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
-  var fixedArray = new List(10);
+  var fixedArray = new List<int>(10);
   for (int i = 0; i < 10; i++) {
     fixedArray[i] = i;
   }