Support experimental annotations for the analysis server spec.

pkg/analysis_server/tool/spec/to_html.dart

Index: pkg/analysis_server/tool/spec/to_html.dart
diff --git a/pkg/analysis_server/tool/spec/to_html.dart b/pkg/analysis_server/tool/spec/to_html.dart
index fa6e341bc08f68d06112647ea0e509e41b9b8784..ac5ec60feed919fef77e13594f7f126cfec6ea62 100644
--- a/pkg/analysis_server/tool/spec/to_html.dart
+++ b/pkg/analysis_server/tool/spec/to_html.dart
@@ -540,6 +540,9 @@ class ToHtmlVisitor extends HierarchicalApiVisitor
 
   @override
   void visitNotification(Notification notification) {
+    if (notification.experimental) {
+      return;
+    }
     dt('notification', () {
       anchor('notification_${notification.longEvent}', () {
         write(notification.longEvent);