improve completion for formal param initializers

pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart

Index: pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
index bdce36175badd5ef816d3120aacd4b67c3ef4b89..7a54c9e9bba0971a89789c3da41314a90b6ab9e6 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
@@ -209,6 +209,13 @@ class _KeywordVisitor extends GeneralizingAstVisitor {
   }
 
   @override
+  visitDefaultFormalParameter(DefaultFormalParameter node) {
+    if (entity == node.defaultValue) {
+      _addExpressionKeywords(node);
+    }
+  }
+
+  @override
   visitExpression(Expression node) {
     _addExpressionKeywords(node);
   }