Update to polymer js version 0.4.1

pkg/observe/test/path_observer_test.dart

Index: pkg/observe/test/path_observer_test.dart
diff --git a/pkg/observe/test/path_observer_test.dart b/pkg/observe/test/path_observer_test.dart
index aae8887b657b2626edab0ffae5d4f0f6c03fcae0..e1225ef6aa7e375f914efe2b0d37e2736d8a0405 100644
--- a/pkg/observe/test/path_observer_test.dart
+++ b/pkg/observe/test/path_observer_test.dart
@@ -72,6 +72,7 @@ main() => dirtyCheckZone().run(() {
       expectPath('foo["b\\"az"]', 'foo["b\\"az"]', 2, [#foo, 'b"az']);
       expectPath("foo['b\\'az']", 'foo["b\'az"]', 2, [#foo, "b'az"]);
       expectPath([#a, #b], 'a.b', 2, [#a, #b]);
+      expectPath([], '', 0, []);
 
       expectPath('.', '<invalid path>', 0);
       expectPath(' . ', '<invalid path>', 0);