Add on_os and on_platform fields.

lib/src/utils.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.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:math' as math;
 
 import 'package:async/async.dart' hide StreamQueue;
 import 'package:crypto/crypto.dart';
@@ skipping 210 matching lines @@
   });
   return result;
 }
 
 /// Returns a new map with all values in both [map1] and [map2].
 ///
 /// If there are conflicting keys, [value] is used to merge them. If it's
 /// not passed, [map2]'s value wins.
 Map mergeMaps(Map map1, Map map2, {value(value1, value2)}) {
   var result = new Map.from(map1);
-  map2.forEach((key, value) {
+  map2.forEach((key, mapValue) {
     if (value == null || !result.containsKey(key)) {
-      result[key] = value;
+      result[key] = mapValue;
     } else {
-      result[key] = value(result[key], value);
+      result[key] = value(result[key], mapValue);
     }
   });
   return result;
 }
 
 /// Like [runZoned], but [zoneValues] are set for the callbacks in
 /// [zoneSpecification] and [onError].
 runZonedWithValues(body(), {Map zoneValues,
     ZoneSpecification zoneSpecification, Function onError}) {
   return runZoned(() {
@@ skipping 193 matching lines @@
       urlSafe: urlSafe, addLineSeparator: addLineSeparator);
 }
 
 /// Returns middleware that nests all requests beneath the URL prefix [beneath].
 shelf.Middleware nestingMiddleware(String beneath) {
   return (handler) {
     var pathHandler = new PathHandler()..add(beneath, handler);
     return pathHandler.handler;
   };
 }