Support for the 'covariant' keyword for formal parameters.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 67c49ed80e6aade3564a4c70a18b69aeca7a6db9..95bca4ce04576169601c83a3d7d8a290249e4329 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -1277,7 +1277,8 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   }
 
   @override
-  void endFormalParameter(Token thisKeyword, FormalParameterType kind) {
+  void endFormalParameter(Token covariantKeyword, Token thisKeyword,
+      FormalParameterType kind) {
     debugEvent("FormalParameter");
     // TODO(ahe): Need beginToken here.
     int charOffset = thisKeyword?.charOffset;