Generate typedef node from the element.

tests/compiler/dart2js/backend_dart/dart_backend_test.dart

 // Copyright (c) 2012, 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 "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import '../mock_compiler.dart';
 import '../mock_libraries.dart';
 import 'package:compiler/compiler.dart';
@@ skipping 196 matching lines @@
 }
 class A {
   static const String a = "5";
   static const String b = "4";
 }
 ''');
   // Class member of typedef-ed function type.
   // Maybe typedef should be included in the result too, but it
   // works fine without it.
   testDart2Dart('''
-typedef void foofunc(arg);
+typedef void foofunc(_0);
 main() {
   new A((arg) {});
 }
 class A {
   A(foofunc this.handler);
   final foofunc handler;
 }
 ''');
 }
 
@@ skipping 434 matching lines @@
   MyFunction myf1;
   mylib.MyFunction myf2;
   new A<int>().f;
   new T();
 
   new mylib.A<int>().f;
   new mylib.T();
 }
 ''';
   var expectedResult = '''
-typedef void MyFunction<T_B extends num>(T_B arg);
+typedef void MyFunction<T_B extends num>(T_B _0);
 class T {}
 class B<T_B> {}
 class A<T_B> extends B<T_B> {
   T_B f;
 }
-typedef void MyFunction_A<T_B extends num>(T_B arg);
+typedef void MyFunction_A<T_B extends num>(T_B _0);
 class T_A {}
 class B_A<T_B> {}
 class A_A<T_B> extends B_A<T_B> {
   T_B f;
 }
 main() {
   MyFunction_A myf1;
   MyFunction myf2;
   new A_A<int>().f;
   new T_A();
@@ skipping 411 matching lines @@
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
   testUnresolvedNamedConstructor1();
   testUnresolvedNamedConstructor2();
   testUnresolvedNamedConstructor3();
   testClassAndNamedMixinDeclarations();
 }