Dispatch with conversion hooks

lib/dom/templates/html/dart2js/html_dart2js.darttemplate

Index: lib/dom/templates/html/dart2js/html_dart2js.darttemplate
diff --git a/lib/dom/templates/html/dart2js/html_dart2js.darttemplate b/lib/dom/templates/html/dart2js/html_dart2js.darttemplate
index 6c07d08ed56b74e05cc6c0434b1eddae9298cc54..a01ac8303396a1d5ce8f61d456899e228aa350eb 100644
--- a/lib/dom/templates/html/dart2js/html_dart2js.darttemplate
+++ b/lib/dom/templates/html/dart2js/html_dart2js.darttemplate
@@ -22,6 +22,7 @@ $!GENERATED_DART_FILES
 #source('../../html/src/Isolates.dart');
 #source('../../html/src/Measurement.dart');
 #source('../../html/src/shared_FactoryProviders.dart');
+#source('../../html/src/dart2js_Conversions.dart');
 #source('../../html/src/dart2js_DOMImplementation.dart');
 #source('../../html/src/dart2js_FactoryProviders.dart');
 #source('../../html/src/dart2js_IDBKeyRangeFactoryProvider.dart');
@@ -44,6 +45,13 @@ _DocumentImpl get _document() native "return document;";
 Element query(String selector) => _document.query(selector);
 ElementList queryAll(String selector) => _document.queryAll(selector);
 
+/// Marker for defaulted arguments.
+class _Default {
+  const _Default();
+}
+
+final _default = const _Default();
+
 // Workaround for tags like <cite> that lack their own Element subclass --
 // Dart issue 1990.
 class _HTMLElementImpl extends _ElementImpl native "*HTMLElement" {