Fix some warnings in the core library identified by the static analyzer.

corelib/src/future.dart

Index: corelib/src/future.dart
diff --git a/corelib/src/future.dart b/corelib/src/future.dart
index 3da2a2585e601b3528026cc285bb89fa7750c6df..9c84680d8e03d9f328d01e355f8da2a25a826b1a 100644
--- a/corelib/src/future.dart
+++ b/corelib/src/future.dart
@@ -201,7 +201,7 @@ class Futures {
     Completer completer = new Completer<List>();
     Future<List> result = completer.future;
     int remaining = futures.length;
-    List<Object> values = new List(futures.length);
+    List values = new List(futures.length);
 
     // As each future completes, put its value into the corresponding
     // position in the list of values.