Updating Polymer to derive from custom elements.

pkg/polymer/test/take_attributes_test.dart

Index: pkg/polymer/test/take_attributes_test.dart
diff --git a/pkg/polymer/test/take_attributes_test.dart b/pkg/polymer/test/take_attributes_test.dart
index a9e409f35a152b7e1479092cb0e3de6ee232c0a8..d714a45e0e754c9933d1ba342da34a5b08a59528 100644
--- a/pkg/polymer/test/take_attributes_test.dart
+++ b/pkg/polymer/test/take_attributes_test.dart
@@ -9,6 +9,8 @@ import 'package:polymer/polymer.dart';
 
 @CustomTag('x-foo')
 class XFoo extends PolymerElement {
+  XFoo.created() : super.created();
+
   @published bool boolean = false;
   @published num number = 42;
   @published String str = "don't panic";
@@ -16,6 +18,8 @@ class XFoo extends PolymerElement {
 
 @CustomTag('x-bar')
 class XBar extends PolymerElement {
+  XBar.created() : super.created();
+
   @observable bool boolean = false;
   @observable num number = 42;
   @observable String str = "don't panic";
@@ -23,21 +27,25 @@ class XBar extends PolymerElement {
 
 @CustomTag('x-zot')
 class XZot extends XBar {
+  XZot.created() : super.created();
   @observable num number = 84;
 }
 
 @CustomTag('x-date')
 class XDate extends PolymerElement {
+  XDate.created() : super.created();
   @observable var value = new DateTime(2013, 9, 25);
 }
 
 @CustomTag('x-array')
 class XArray extends PolymerElement {
+  XArray.created() : super.created();
   @observable List values;
 }
 
 @CustomTag('x-obj')
 class XObj extends PolymerElement {
+  XObj.created() : super.created();
   @observable var values = {};
 }