Annotate optional parameter inferred types in front end test cases.

pkg/analyzer/test/src/task/strong/front_end_inference_test.dart

Index: pkg/analyzer/test/src/task/strong/front_end_inference_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/front_end_inference_test.dart b/pkg/analyzer/test/src/task/strong/front_end_inference_test.dart
index 0d5db321665922de23708ad2bee6960fb539539f..afb9c1e37700a2a9bf27f6949e70b7fadc909f36 100644
--- a/pkg/analyzer/test/src/task/strong/front_end_inference_test.dart
+++ b/pkg/analyzer/test/src/task/strong/front_end_inference_test.dart
@@ -319,7 +319,12 @@ class _InstrumentationVisitor extends RecursiveAstVisitor<Null> {
         List<FormalParameter> parameters = node.parameters.parameters;
         for (int i = 0; i < parameters.length; i++) {
           FormalParameter parameter = parameters[i];
-          if (parameter is SimpleFormalParameter && parameter.type == null) {
+          NormalFormalParameter normalParameter =
+              parameter is DefaultFormalParameter
+                  ? parameter.parameter
+                  : parameter;
+          if (normalParameter is SimpleFormalParameter &&
+              normalParameter.type == null) {
             _recordType(parameter.offset, type.parameters[i].type);
           }
         }