Suggest covariant in parameter lists

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 64caca0ebccb0da793e6555d3ccbed4185b1359f..433ea389aebb916f58442e851f01ff0b9b157fbe 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
@@ -253,6 +253,14 @@ class _KeywordVisitor extends GeneralizingAstVisitor {
     if (constructorDeclaration != null) {
       _addSuggestions([Keyword.THIS]);
     }
+    if (entity is Token && (entity as Token).type == TokenType.CLOSE_PAREN) {
+      _addSuggestion(Keyword.COVARIANT);
+    } else if (entity is FormalParameter) {
+      Token beginToken = (entity as FormalParameter).beginToken;
+      if (beginToken != null && request.target.offset == beginToken.end) {
+        _addSuggestion(Keyword.COVARIANT);
+      }
+    }
   }
 
   @override