First cut at behaviors. This just implements the lifecycle methodsportion. We may get the rest for …

lib/src/common/polymer_mixin.dart

Index: lib/src/common/polymer_mixin.dart
diff --git a/lib/src/common/polymer_mixin.dart b/lib/src/common/polymer_mixin.dart
index c16678a9432bd39d4b047e650ec8ceb640c55185..b813acd8fd505ca55576ba9dc9a1d923b4ebb1fd 100644
--- a/lib/src/common/polymer_mixin.dart
+++ b/lib/src/common/polymer_mixin.dart
@@ -6,11 +6,12 @@ library polymer.src.common.polymer_js_proxy;
 import 'dart:html';
 import 'dart:js';
 import 'package:polymer_interop/polymer_interop.dart' show Polymer, PolymerDom;
+import 'package:web_components/web_components.dart';
 import 'js_proxy.dart';
 
 
 /// Basic api for re-using the polymer js prototypes.
-abstract class PolymerMixin implements JsProxy {
+abstract class PolymerMixin implements JsProxy, CustomElementProxyMixin {
   JsObject _proxy;
 
   JsObject get jsElement {