Use `Function` as function type syntax.

pkg/compiler/lib/src/helpers/helpers.dart

 // Copyright (c) 2014, 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.
 
 /// Library for debugging helpers. The unittest analyze_unused_test checks that
 /// the helper are not used in production code.
 
 library dart2js.helpers;
 
 import '../common.dart';
@@ skipping 19 matching lines @@
 void enableDebugMode() {
   DEBUG_MODE = true;
 }
 
 class _DebugIndentation extends Indentation {
   final String indentationUnit = " ";
 }
 
 _DebugIndentation _indentation = new _DebugIndentation();
 
-/// Function signature of [debugPrint].
-typedef DebugPrint(s);
-
 /// If [DEBUG_PRINT_ENABLED] is `true` print [s] using the current identation.
-DebugPrint get debugPrint {
+void Function(dynamic s) get debugPrint {
   enableDebugMode();
   // TODO(johnniwinther): Maybe disable debug mode after the call.
   return _debugPrint;
 }
 
 /// Implementation of [debugPrint].
-_debugPrint(s) {
+void _debugPrint(s) {
   if (DEBUG_PRINT_ENABLED) print('${_indentation.indentation}$s');
 }
 
-/// Function signature of [debugWrapPrint].
-typedef DebugWrapPrint(s, f());
-
 /// Wraps the call to [f] with a print of 'start:$s' and 'end:$s' incrementing
 /// the current indentation used by [debugPrint] during the execution of [f].
 ///
 /// Use this to get a tree-like debug printout for nested calls.
-DebugWrapPrint get debugWrapPrint {
+dynamic Function(dynamic s, dynamic Function() f) get debugWrapPrint {
   enableDebugMode();
   return _debugWrapPrint;
 }
 
 /// Implementation of [debugWrapPrint].
 _debugWrapPrint(s, f()) {
   debugPrint('start:$s');
   var result = _indentation.indentBlock(f);
   debugPrint('end:$s');
   return result;
 }
 
 /// Dummy method to mark breakpoints.
 debugBreak() {
   enableDebugMode();
 }
 
 /// Function signature of [reportHere].
 typedef ReportHere(
     DiagnosticReporter reporter, Spannable node, String debugMessage);
 
 /// Print a message with a source location.
-ReportHere get reportHere {
+dynamic Function(DiagnosticReporter, Spannable node, String debugMessage)
+    get reportHere {
   enableDebugMode();
   return _reportHere;
 }
 
 /// Implementation of [reportHere]
 _reportHere(DiagnosticReporter reporter, Spannable node, String debugMessage) {
   reporter
       .reportInfo(node, MessageKind.GENERIC, {'text': 'HERE: $debugMessage'});
 }
 
@@ skipping 38 matching lines @@
       if (printTrace) {
         trace(msg);
       } else {
         debugPrint(msg);
       }
     }
     return true;
   }
   return false;
 }