Refactor fuzzy arrow hints.

pkg/dev_compiler/lib/src/js_ast/type_printer.dart

Index: pkg/dev_compiler/lib/src/js_ast/type_printer.dart
diff --git a/pkg/dev_compiler/lib/src/js_ast/type_printer.dart b/pkg/dev_compiler/lib/src/js_ast/type_printer.dart
index 35e7be6379cc56a07777da85954fc397387cf662..ff859aa6c942a5fd50d620769d1420596112616a 100644
--- a/pkg/dev_compiler/lib/src/js_ast/type_printer.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/type_printer.dart
@@ -8,7 +8,8 @@ abstract class _TypePrinterBase implements TypeRefVisitor {
   void out(String s);
   void visit(Node node);
 
-  void outSeparated(String separator, Iterable items, [action(dynamic item)]) {
+  void outSeparated<T extends Node>(String separator, Iterable<T> items,
+      [action(T item)]) {
     action ??= visit;
     var first = true;
     for (var item in items) {