Fix some corelib tests.

tests/corelib/list_map_test.dart

Index: tests/corelib/list_map_test.dart
diff --git a/tests/corelib/list_map_test.dart b/tests/corelib/list_map_test.dart
index 8bd05eb1c64969e2e3f3f7da753315797793ecd2..947f40ad3d3cc5f5d723fbb556599cf4b74ceaea 100644
--- a/tests/corelib/list_map_test.dart
+++ b/tests/corelib/list_map_test.dart
@@ -20,7 +20,7 @@ void testOperations() {
   // Function that reverses l and r lists when used to map.
   int rev(x) => 11 - x;
   // A base list that starts out like l, but isn't const.
-  Iterable base = l.map((x) => x).toList();
+  List base = l.map((x) => x).toList();
 
   Iterable reversed = l.map(rev);