big update to observe, template_binding, polymer

pkg/polymer/test/custom_event_test.dart

Index: pkg/polymer/test/custom_event_test.dart
diff --git a/pkg/polymer/test/custom_event_test.dart b/pkg/polymer/test/custom_event_test.dart
index eef68e09a3d723ee166dca378b0f9b700f7be03f..08c45af96fbaa388acc9f850ba4e065f626ef363 100644
--- a/pkg/polymer/test/custom_event_test.dart
+++ b/pkg/polymer/test/custom_event_test.dart
@@ -53,10 +53,10 @@ main() {
     final fooBar = testComp.fooBar;
 
     final binding = nodeBind(fooBar).bindings['on-barbaz'];
-    expect(binding, isNotNull, reason: 'on-barbaz event should be bound');
+    expect(binding is Bindable, true,
+        reason: 'on-barbaz event should be bound');
 
-    expect(binding.model is! StreamSubscription, true,
-        reason: 'event bindings should not be a StreamSubscription');
+    expect(binding.value, null, reason: 'event bindings do not have value');
 
     fooBar.fireFoo(123);
     fooBar.fireBarBaz(42);