extract field formal contributor from prefixed element contributor

pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart

Index: pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
diff --git a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
index 2b73a30da3202ad71d6098f3f15b2402bff9ab1f..014c2708084653a14d181209279e5efb528ecd96 100644
--- a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
+++ b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
@@ -10,6 +10,7 @@ import 'package:analysis_server/src/provisional/completion/dart/completion_dart.
 import 'package:analysis_server/src/services/completion/dart/arglist_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/combinator_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
+import 'package:analysis_server/src/services/completion/dart/field_formal_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/keyword_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/uri_contributor.dart';
 import 'package:plugin/plugin.dart';
@@ -72,6 +73,8 @@ class DartCompletionPlugin implements Plugin {
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new CombinatorContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
+        () => new FieldFormalContributor());
+    registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new KeywordContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new UriContributor());