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 03930aaa949107fbb365311af067f7292ad018ae..a0cbc0b7c6299e1d4bcca589560b10400ca09805 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/dart_printer.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 "],
 };