Deprecate use of timezones.

runtime/bin/http_impl.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.
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders() : _headers = new Map<String, List<String>>();
 
   List<String> operator[](String name) {
     name = name.toLowerCase();
     return _headers[name];
@@ skipping 73 matching lines @@
       } catch (Exception e) {
         return null;
       }
     }
     return null;
   }
 
   void set date(Date date) {
     _checkMutable();
     // Format "Date" header with date in Greenwich Mean Time (GMT).
-    String formatted =
-        _HttpUtils.formatDate(expires.changeTimeZone(new TimeZone.utc()));
+    String formatted = _HttpUtils.formatDate(expires.toUtc());
     _set("date", formatted);
   }
 
   Date get expires() {
     List<String> values = _headers["expires"];
     if (values != null) {
       try {
         return _HttpUtils.parseDate(values[0]);
       } catch (Exception e) {
         return null;
       }
     }
     return null;
   }
 
   void set expires(Date expires) {
     _checkMutable();
     // Format "Expires" header with date in Greenwich Mean Time (GMT).
-    String formatted =
-        _HttpUtils.formatDate(expires.changeTimeZone(new TimeZone.utc()));
+    String formatted = _HttpUtils.formatDate(expires.toUtc());
     _set("expires", formatted);
   }
 
   ContentType get contentType() {
     var values = _headers["content-type"];
     if (values != null) {
       return new ContentType.fromString(values[0]);
     } else {
       return new ContentType();
     }
@@ skipping 1700 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }