dart2js: Don't use "void" as field.

pkg/compiler/lib/src/js_backend/namer.dart

 // Copyright (c) 2011, 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 js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  *
  * Names are generated through three stages:
@@ skipping 1373 matching lines @@
   String get operatorIsPrefix => r'$is';
 
   String get operatorAsPrefix => r'$as';
 
   String get operatorSignature => r'$signature';
 
   String get typedefTag => r'typedef';
 
   String get functionTypeTag => r'func';
 
-  String get functionTypeVoidReturnTag => r'void';
+  String get functionTypeVoidReturnTag => r'v';
 
   String get functionTypeReturnTypeTag => r'ret';
 
   String get functionTypeRequiredParametersTag => r'args';
 
   String get functionTypeOptionalParametersTag => r'opt';
 
   String get functionTypeNamedParametersTag => r'named';
 
   Map<FunctionType, jsAst.Name> functionTypeNameMap =
@@ skipping 588 matching lines @@
       }
     }
   }
 }
 
 enum NamingScope {
   global,
   instance,
   constant
 }