Update to use one less proxy per element

lib/src/common/polymer_descriptor.dart

Index: lib/src/common/polymer_descriptor.dart
diff --git a/lib/src/common/polymer_descriptor.dart b/lib/src/common/polymer_descriptor.dart
index b0c8c10da58d6aaeab68c30b7f88bf1b46468664..147155d12e5bc633cd532f87f2347b265d017130 100644
--- a/lib/src/common/polymer_descriptor.dart
+++ b/lib/src/common/polymer_descriptor.dart
@@ -231,10 +231,11 @@ Iterable<JsObject> _buildBehaviorsList(Type type) {
     behaviorStack.add(behavior);
   }
 
-  return behaviorStack.map((ClassMirror behavior) {
-    BehaviorAnnotation meta = behavior.metadata.firstWhere(_isBehavior);
-    return meta.getBehavior(behavior.reflectedType);
-  });
+  return <JsObject>[_polymerDart['InteropBehavior']]
+    ..addAll(behaviorStack.map((ClassMirror behavior) {
+      BehaviorAnnotation meta = behavior.metadata.firstWhere(_isBehavior);
+      return meta.getBehavior(behavior.reflectedType);
+    }));
 }
 
 // Throws an error about expected mixins that must precede the [clazz] mixin.