[polymer.dart] fix *Changed observers inheriting

pkg/polymer/test/publish_attributes_test.dart

Index: pkg/polymer/test/publish_attributes_test.dart
diff --git a/pkg/polymer/test/publish_attributes_test.dart b/pkg/polymer/test/publish_attributes_test.dart
index b22132e3cc26060dd81d38bc1d761fdfb790ae43..8701a7b080e5b245dbd0f948fff3bc7403b28664 100644
--- a/pkg/polymer/test/publish_attributes_test.dart
+++ b/pkg/polymer/test/publish_attributes_test.dart
@@ -37,10 +37,21 @@ class XSquid extends XZot {
   XSquid.created() : super.created();
 
   @published int baz = 13;
-  @published int zot = 5;
+  @published int zot = 3;
   @published int squid = 7;
 }
 
+// Test inherited "attriubtes"
+class XBaz extends PolymerElement {
+  XBaz.created() : super.created();
+  @observable int qux = 13;
+}
+
+@CustomTag('x-qux')
+class XQux extends XBaz {
+  XQux.created() : super.created();
+}
+
 main() {
   initPolymer();
   useHtmlConfiguration();
@@ -55,5 +66,6 @@ main() {
     expect(published('x-bar'), [#Foo, #baz, #Bar]);
     expect(published('x-zot'), [#Foo, #baz, #Bar, #zot]);
     expect(published('x-squid'), [#Foo, #baz, #Bar, #zot, #squid]);
+    expect(published('x-qux'), [#qux]);
   });
 }