Use `Function` as function type syntax.

pkg/compiler/lib/src/js_backend/constant_emitter.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 '../common.dart';
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../io/code_output.dart';
@@ skipping 15 matching lines @@
  * constants should be inlined or not.
  */
 class ConstantEmitter implements ConstantValueVisitor<jsAst.Expression, Null> {
   // Matches blank lines, comment lines and trailing comments that can't be part
   // of a string.
   static final RegExp COMMENT_RE =
       new RegExp(r'''^ *(//.*)?\n|  *//[^''"\n]*$''', multiLine: true);
 
   final Compiler compiler;
   final Namer namer;
-  final _ConstantReferenceGenerator constantReferenceGenerator;
-  final _ConstantListGenerator makeConstantList;
+  final jsAst.Expression Function(ConstantValue) constantReferenceGenerator;
+  final jsAst.Expression Function(jsAst.Expression array) makeConstantList;
 
   /**
    * The given [constantReferenceGenerator] function must, when invoked with a
    * constant, either return a reference or return its literal expression if it
    * can be inlined.
    */
   ConstantEmitter(
       this.compiler,
       this.namer,
-      jsAst.Expression this.constantReferenceGenerator(ConstantValue constant),
+      jsAst.Expression Function(ConstantValue) this.constantReferenceGenerator,
       this.makeConstantList);
 
   DiagnosticReporter get reporter => compiler.reporter;
 
   /**
    * Constructs a literal expression that evaluates to the constant. Uses a
    * canonical name unless the constant can be emitted multiple times (as for
    * numbers and strings).
    */
   jsAst.Expression generate(ConstantValue constant) {
@@ skipping 291 matching lines @@
       arguments.add(rtiEncoder.getTypeRepresentation(argument, unexpected));
     }
     return new jsAst.ArrayInitializer(arguments);
   }
 
   @override
   jsAst.Expression visitDeferred(DeferredConstantValue constant, [_]) {
     return constantReferenceGenerator(constant.referenced);
   }
 }