Implements frame sniffer to watch iframe loading state.

chrome/app/generated_resources.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!--
 This file contains definitions of resources that will be translated for each
 locale.  The variables is_win, is_macosx, is_linux, and is_posix are available
 for making strings OS specific.  Other platform defines such as use_titlecase
 are declared in build/common.gypi.
 -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
@@ skipping 13261 matching lines @@
       </message>
       <message name="IDS_LOGIN_ERROR_KEYBOARD_SWITCH_HINT" desc="A hint text for the login and lock screens">
         Hit Shift-Alt to switch keyboard layout
       </message>
       <message name="IDS_LOGIN_ERROR_CAPTIVE_PORTAL" desc="An error message shown when we suggest that user may be behind the captive portal.">
         Before signing in, please start a Guest session to activate the network <ph name="NETWORK_ID">$1<ex>Public Wifi</ex></ph>
       </message>
       <message name="IDS_LOGIN_FIX_CAPTIVE_PORTAL" desc="An link text to fix Internet connection (captive portal) in guest mode.">
         Start a Guest session
       </message>
+      <message name="IDS_LOGIN_MAYBE_CAPTIVE_PORTAL" desc="An offline message shown when we suggest that user may be behind the captive portal.">
+        Connected to a network, but still can't sign in? You might be on a network that requires a web-based authentication. Start a guest browsing session (if available) and see if a network log-in page appears. Once you're logged in to the network and are able to visit different web pages, exit the guest session and try signing in again.
+      </message>
       <message name="IDS_LOGIN_ERROR_CAPTIVE_PORTAL_NO_GUEST_MODE" desc="An error message shown when we suggest that user may be behind the captive portal but Guest mode is disabled.">
         Your password cannot be verified on this current network. Please select another network.
       </message>
       <message name="IDS_NOTIFICATION_PANEL_TITLE" desc="Text for the title of the notification panel.">
         Notifications
       </message>
       <message name="IDS_LOGIN_OFFLINE_TITLE" desc="Title of an offline message that shows up in OOBE sign-in screen.">
         You are currently offline
       </message>
       <message name="IDS_LOGIN_OFFLINE_MESSAGE" desc="An offline message that shows up in OOBE sign-in screen.">
@@ skipping 346 matching lines @@
     </messages>
     <structures fallback_to_english="true">
       <!-- Make sure these stay in sync with the structures in generated_resources.grd. -->
       <structure name="IDD_CHROME_FRAME_FIND_DIALOG" file="cf_resources.rc" type="dialog" >
       </structure>
       <structure name="IDD_CHROME_FRAME_READY_PROMPT" file="cf_resources.rc" type="dialog" >
       </structure>
     </structures>
   </release>
 </grit>