port polymer data binding tests

pkg/polymer/lib/src/instance.dart

Index: pkg/polymer/lib/src/instance.dart
diff --git a/pkg/polymer/lib/src/instance.dart b/pkg/polymer/lib/src/instance.dart
index f0bff99c4637274b00dd6c5d15419547f71b76d9..f2f1f873e4e8f1a077fb354c253fcdb7127074f8 100644
--- a/pkg/polymer/lib/src/instance.dart
+++ b/pkg/polymer/lib/src/instance.dart
@@ -509,15 +509,13 @@ class PolymerElement extends CustomElement with ObservableMixin {
   }
 
   void observeProperty(String name, Symbol method) {
-    final self = reflect(this);
-    _observe(name, (value, old) => self.invoke(method, [old]));
+    _observe(name, (value, old) => _invoke(method, [old]));
   }
 
   void observeBoth(String name, Symbol methodName) {
-    final self = reflect(this);
     _observe(name, (value, old) {
       reflectPropertyToAttribute(name);
-      self.invoke(methodName, [old]);
+      _invoke(methodName, [old]);
     });
   }
 
@@ -646,10 +644,18 @@ class PolymerElement extends CustomElement with ObservableMixin {
     bool log = _eventsLog.isLoggable(Level.INFO);
     if (log) _eventsLog.info('>>> [$localName]: dispatch $methodName');
 
-    // TODO(sigmund): consider making event listeners list all arguments
-    // explicitly. Unless VM mirrors are optimized first, this reflectClass call
-    // will be expensive once custom elements extend directly from Element (see
-    // dartbug.com/11108).
+    _invoke(methodName, args);
+
+    if (log) _eventsLog.info('<<< [$localName]: dispatch $methodName');
+
+    // TODO(jmesserly): workaround for HTML events not supporting zones.
+    performMicrotaskCheckpoint();
+  }
+
+  InstanceMirror _invoke(Symbol methodName, List args) {
+    // TODO(sigmund): consider making callbacks list all arguments
+    // explicitly. Unless VM mirrors are optimized first, this will be expensive
+    // once custom elements extend directly from Element (see issue 11108).
     var self = reflect(this);
     var method = self.type.methods[methodName];
     if (method != null) {
@@ -659,12 +665,7 @@ class PolymerElement extends CustomElement with ObservableMixin {
       // them appart from named arguments (see http://dartbug.com/11334)
       args.length = method.parameters.where((p) => !p.isOptional).length;
     }
-    self.invoke(methodName, args);
-
-    if (log) _eventsLog.info('<<< [$localName]: dispatch $methodName');
-
-    // TODO(jmesserly): workaround for HTML events not supporting zones.
-    performMicrotaskCheckpoint();
+    return self.invoke(methodName, args);
   }
 
   void instanceEventListener(Event event) {