Emit declarations for typedefs that are needed by reflection.

tests/compiler/dart2js/analyze_unused_dart2js_test.dart

Index: tests/compiler/dart2js/analyze_unused_dart2js_test.dart
diff --git a/tests/compiler/dart2js/analyze_unused_dart2js_test.dart b/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
index 699beff2a95abaf55bd4192bf111c74ff6728ac2..97ef096dc240320157e5a96188c907ab6198cf68 100644
--- a/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
+++ b/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
@@ -22,6 +22,10 @@ const Map<String, List<String>> WHITE_LIST = const {
   // Some things in dart_printer are not yet used
   "implementation/dart_backend/backend_ast_nodes.dart" : const [" is never "],
 
+  // dart2js uses only the encoding functions, the decoding functions are used
+  // from the generated code.
+  "implementation/runtime_data.dart": const [" is never "],
+
   // Setlet implements the Set interface: Issue 18959.
   "implementation/util/setlet.dart": const [" is never "],
 };