[polymer] add a new API to create an element without polymer-element in HTML

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 96c8698d2395b19f69a626cf01071d8172a0c8b1..4dcca03e6fc4c60c0160607b0dd1cf6fa6bfa05e 100644
--- a/pkg/polymer/lib/src/instance.dart
+++ b/pkg/polymer/lib/src/instance.dart
@@ -79,6 +79,26 @@ abstract class Polymer implements Element, Observable, NodeBindExtension {
     (js.context['Polymer'] as JsFunction).apply([name]);
   }
 
+  /// Register a custom element that has no associated `<polymer-element>`.
+  /// Unlike [register] this will always perform synchronous registration and
+  /// by the time this method returns the element will be available using
+  /// [document.createElement] or by modifying the HTML to include the element.
+  static void registerSync(String name, Type type,
+      {String extendsTag, Document doc, Node template}) {
+
+    // Our normal registration, this will queue up the name->type association.
+    register(name, type);
+
+    // Build a polymer-element and initialize it to register
+    if (doc == null) doc = document;
+    var poly = doc.createElement('polymer-element');
+    poly.attributes['name'] = name;
+    if (extendsTag != null) poly.attributes['extends'] = extendsTag;
+    if (template != null) poly.append(template);
+
+    new JsObject.fromBrowserObject(poly).callMethod('init');
+  }
+
   /// The one syntax to rule them all.
   static final BindingDelegate _polymerSyntax =
       new PolymerExpressionsWithEvents();