add -f option to force a client update

src/platform/dev/autoupdate.py

 # Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from buildutil import BuildObject
 from xml.dom import minidom
 
 import os
 import web
 
@@ skipping 77 matching lines @@
     web.debug(cmd)
     return os.popen(cmd).read()
 
   def HandleUpdatePing(self, data):
     update_dom = minidom.parseString(data)
     root = update_dom.firstChild
     query = root.getElementsByTagName("o:app")[0]
     client_version = query.attributes['version'].value
     latest_image_path = self.GetLatestImagePath();
     latest_version = self.GetLatestVersion(latest_image_path);
-    if not self.CanUpdate(client_version, latest_version):
+    if client_version != "ForcedUpdate" and not self.CanUpdate(client_version, latest_version):
       web.debug("no update")
       return self.GetNoUpdatePayload()
 
     web.debug("update found %s " % latest_version)
     ok = self.BuildUpdateImage(latest_image_path)
     if ok != True:
       web.debug("Failed to build an update image")
       return self.GetNoUpdatePayload()
 
     hash = self.GetHash("%s/update.gz" % self.static_dir)
     size = self.GetSize("%s/update.gz" % self.static_dir)
     hostname = web.ctx.host
     url = "http://%s/static/update.gz" % hostname
     return self.GetUpdatePayload(hash, size, url)