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

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 f4457caeb8275be5c79b115b2f376c15e55a6d99..ba5ab24f197b5320ce22c27695c1b7a71e86e283 100644
--- a/lib/src/common/polymer_descriptor.dart
+++ b/lib/src/common/polymer_descriptor.dart
@@ -5,6 +5,7 @@ library polymer.src.micro.properties;
 
 import 'dart:js';
 import 'package:reflectable/reflectable.dart';
+import 'behavior.dart';
 import 'declarations.dart';
 import 'js_proxy.dart';
 import 'property.dart';
@@ -20,9 +21,10 @@ JsObject createPolymerDescriptor(Type type, PolymerRegister annotation) {
     'is': annotation.tagName,
     'extends': annotation.extendsTag,
     'hostAttributes': annotation.hostAttributes,
-    'properties': buildPropertiesObject(type),
+    'properties': _buildPropertiesObject(type),
     'observers': _buildObserversObject(type),
     'listeners': _buildListenersObject(type),
+    'behaviors': _buildBehaviorsList(type),
     '__isPolymerDart__': true,
   };
   _setupLifecycleMethods(type, object);
@@ -44,7 +46,7 @@ Map<String, DeclarationMirror> propertyDeclarationsFor(Type type) {
 }
 
 // Set up the `properties` descriptor object.
-Map buildPropertiesObject(Type type) {
+Map _buildPropertiesObject(Type type) {
   var declarations = propertyDeclarationsFor(type);
   var properties = {};
   declarations.forEach((String name, DeclarationMirror declaration) {
@@ -187,6 +189,23 @@ Map _getPropertyInfoForType(Type type, DeclarationMirror declaration) {
   return property;
 }
 
+/// List of [JsObjects]s representing the behaviors for an element.
+List<JsObject> _buildBehaviorsList(Type type) {
+  var behaviors = <JsObject>[];
+
+  isBehavior(instance) => instance is BehaviorInterface;
+
+  var interfaces = mixinsFor(type, jsProxyReflectable,

[Siggi Cherem (dart-lang), 2015/08/12 22:43:15]

Seems like we are visiting each behavior annotation twice. I wonder if it's
worth adding a "forEach" besides the current query APIs so you can do some extra
work while walking up the chain:

mixinForEach(type, jsProxyReflectable, (mixin) {
  BehaviorAnnotation meta = mixin.metadata.firstWhere(isBehavior,
      orElse: () => null);
  if (meta != null) behaviors.add(meta.getBehavior(mixin.reflectedType));
});

WDYT?

[jakemac, 2015/08/13 17:50:45]

I didn't add mixinForEach, but I did modify it to only check the annotations
once using similar logic.

+      where: (ClassMirror mixin) => mixin.metadata.any(isBehavior));
+  for (var interface in interfaces) {
+    behaviors.add(
+        (interface.metadata.firstWhere(isBehavior) as BehaviorInterface)
+            .getBehavior(interface.reflectedType));
+  }
+
+  return behaviors.isEmpty ? null : behaviors;
+}
+
 /// Given a [Type] return the [JsObject] representation of that type.
 /// TODO(jakemac): Make this more robust, specifically around Lists.
 dynamic jsType(Type type) {