Add an experimental domain

pkg/analysis_server/lib/src/plugin/server_plugin.dart

Index: pkg/analysis_server/lib/src/plugin/server_plugin.dart
diff --git a/pkg/analysis_server/lib/src/plugin/server_plugin.dart b/pkg/analysis_server/lib/src/plugin/server_plugin.dart
index 5862b4a638da23c315c9854114e97f7746c47280..487c8f5ace023ef02f1b68af5bb4acc1f3b82e46 100644
--- a/pkg/analysis_server/lib/src/plugin/server_plugin.dart
+++ b/pkg/analysis_server/lib/src/plugin/server_plugin.dart
@@ -21,6 +21,7 @@ import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analysis_server/src/domain_completion.dart';
 import 'package:analysis_server/src/domain_execution.dart';
+import 'package:analysis_server/src/domain_experimental.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/domains/analysis/navigation_dart.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences_dart.dart';
@@ -304,6 +305,8 @@ class ServerPlugin implements Plugin {
         (AnalysisServer server) => new CompletionDomainHandler(server));
     registerExtension(domainId,
         (AnalysisServer server) => new ExecutionDomainHandler(server));
+    registerExtension(domainId,
+        (AnalysisServer server) => new ExperimentalDomainHandler(server));
     //
     // Register fix contributors.
     //