Added "Use an autoconfiguration URL" checkbox in proxy tab

chrome/app/chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- ChromeOS-specific strings (included from generated_resources.grd).
      Everything in this file is wrapped in <if expr="pp_ifdef('chromeos')">. -->
 <grit-part>
   <!-- Idle logout dialog for retail mode -->
   <message name="IDS_IDLE_LOGOUT_TITLE" desc="Dialog title for the idle logout dialog. Used in retail mode only.">
     Are you still there?
   </message>
   <message name="IDS_IDLE_LOGOUT_WARNING_RESTART" desc="Restart label for the idle logout dialog. Used in retail mode only..">
     This computer will reset in <ph name="LOGOUT_TIME_LEFT">$1<ex>20</ex></ph> seconds.
@@ skipping 2333 matching lines @@
   </message>
   <message name="IDS_PROXY_FTP_PROXY" desc="Label for the ftp proxy box.">
     FTP proxy
   </message>
   <message name="IDS_PROXY_SOCKS_HOST" desc="Label for the SOCKS host box.">
     SOCKS host
   </message>
   <message name="IDS_PROXY_AUTOMATIC" desc="Radio to select configuring from a URL.">
     Automatic proxy configuration
   </message>
   <message name="IDS_PROXY_CONFIG_URL" desc="Label for the proxy config URL box.">

[Dan Beam, 2013/03/29 22:23:34]

you should probably rename this and update the desc as well, i.e.
IDS_PROXY_USE_AUTOCONFIG_URL and "Label for the checkbox that controls whether
to use an autoconfiguration URL."

-    Autoconfiguration URL
+    Use an autoconfiguration URL
   </message>
   <message name="IDS_PROXY_ADVANCED_CONFIG" desc="Label for the Advanced Proxy.">
     Advanced Configuration
   </message>
   <message name="IDS_PROXY_ADD_HOST" desc="Label for the Add host button.">
     Add
   </message>
   <message name="IDS_PROXY_REMOVE_HOST" desc="Label for the Remove host button.">
     Remove
   </message>
@@ skipping 1213 matching lines @@
   <message name="IDS_KIOSK_APP_ERROR_UNABLE_TO_MOUNT" desc="Error message used when a kiosk app fails to launch due to cryptohome error.">
     Kryptonite! The cryptohome for the kiosk application could not be mounted.
   </message>
   <message name="IDS_KIOSK_APP_ERROR_UNABLE_TO_INSTALL" desc="Error message used when a kiosk app fails to launch due to install failure.">
     Kiosk application could not be installed.
   </message>
   <message name="IDS_KIOSK_APP_ERROR_USER_CANCEL" desc="Error message used when a kiosk app launch is canceled by user.">
     Kiosk application launch canceled.
   </message>
 </grit-part>