Use `Function` as function type syntax.

pkg/compiler/lib/src/js_emitter/full_emitter/declarations.dart

 // Copyright (c) 2013, 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.
 
 part of dart2js.js_emitter.full_emitter;
 
 /// Enables debugging of fast/slow objects using V8-specific primitives.
 const DEBUG_FAST_OBJECTS = false;
 
-/**
- * Call-back for adding property with [name] and [value].
- */
-typedef jsAst.Property AddPropertyFunction(
-    jsAst.Name name, jsAst.Expression value);
-
 // Compact field specifications.  The format of the field specification is
 // <accessorName>:<fieldName><suffix> where the suffix and accessor name
 // prefix are optional.  The suffix directs the generation of getter and
 // setter methods.  Each of the getter and setter has two bits to determine
 // the calling convention.  Setter listed below, getter is similar.
 //
 //     00: no setter
 //     01: function(value) { this.field = value; }
 //     10: function(receiver, value) { receiver.field = value; }
 //     11: function(receiver, value) { this.field = value; }
 //
 // The suffix encodes 4 bits using three ASCII ranges of non-identifier
 // characters.
 const FIELD_CODE_CHARACTERS = r"<=>?@{|}~%&'()*";
 const NO_FIELD_CODE = 0;
 const FIRST_FIELD_CODE = 1;
 const RANGE1_FIRST = 0x3c; //  <=>?@    encodes 1..5
 const RANGE1_LAST = 0x40;
 const RANGE2_FIRST = 0x7b; //  {|}~     encodes 6..9
 const RANGE2_LAST = 0x7e;
 const RANGE3_FIRST = 0x25; //  %&'()*+  encodes 10..16
 const RANGE3_LAST = 0x2b;