Partially rollback noSuchMethod for UnknownElement until we figure out code size issue

lib/dom/templates/html/impl/impl_UnknownElement.darttemplate

Index: lib/dom/templates/html/impl/impl_UnknownElement.darttemplate
diff --git a/lib/dom/templates/html/impl/impl_UnknownElement.darttemplate b/lib/dom/templates/html/impl/impl_UnknownElement.darttemplate
index 0a4a898ddd7443e14a6d792761e687a558af0a82..bf90047d785d096097b5f8b8a3ec9992000987b3 100644
--- a/lib/dom/templates/html/impl/impl_UnknownElement.darttemplate
+++ b/lib/dom/templates/html/impl/impl_UnknownElement.darttemplate
@@ -11,6 +11,7 @@ $!MEMBERS
   // Hooks to support custom WebComponents.
   var xtag;
 
+$if DARTIUM
   noSuchMethod(String name, List args) {
     if (dynamicUnknownElementDispatcher == null) {
       throw new NoSuchMethodException(this, name, args);
@@ -18,4 +19,7 @@ $!MEMBERS
       return dynamicUnknownElementDispatcher(this, name, args);
     }
   }
+$else
+  // TODO(vsm): Implement noSuchMethod or similar for dart2js.
+$endif
 }