Annotate optional parameter inferred types in front end test cases.

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

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
@@ skipping 301 matching lines @@
   visitFunctionExpression(FunctionExpression node) {
     super.visitFunctionExpression(node);
     if (node.parent is! FunctionDeclaration) {
       DartType type = node.staticType;
       if (type is FunctionType) {
         _instrumentation.record(uri, node.offset, 'returnType',
             new _InstrumentationValueForType(type.returnType, elementNamer));
         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);
           }
         }
       }
     }
   }
 
   @override
   visitFunctionExpressionInvocation(FunctionExpressionInvocation node) {
     super.visitFunctionExpressionInvocation(node);
@@ skipping 160 matching lines @@
 
   /// Based on DDC code generator's `_recoverTypeArguments`
   Iterable<DartType> _recoverTypeArguments(FunctionType g, FunctionType f) {
     assert(identical(g.element, f.element));
     assert(g.typeFormals.isNotEmpty && f.typeFormals.isEmpty);
     assert(g.typeFormals.length + g.typeArguments.length ==
         f.typeArguments.length);
     return f.typeArguments.skip(g.typeArguments.length);
   }
 }