Reland: Show message center on lock screen

ui/strings/ui_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. Specifically, these are UI strings that are used by app/ that
 need to be translated for each locale.-->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
   <outputs>
     <!-- TODO add each of your output files.  Modify the three below, and add
@@ skipping 587 matching lines @@
       <!-- Message center -->
       <message name="IDS_MESSAGE_CENTER_ACCESSIBLE_NAME" desc="The accessible name for the Notification Center window.">
         Notification Center
       </message>
       <message name="IDS_MESSAGE_CENTER_NOTIFIER_DISABLE" desc="The menu entry for disabling a notifier from a notification.">
         Disable notifications from <ph name="notifier_name">$1<ex>Notification Galore!</ex></ph>
       </message>
       <message name="IDS_MESSAGE_CENTER_FOOTER_TITLE" desc="The label in the footer of the message center">
         Notifications
       </message>
+      <message name="IDS_MESSAGE_CENTER_FOOTER_LOCKSCREEN" desc="The label in the footer of the message center on lock screen">
+        Sign in to view your notifications
+      </message>
       <message name="IDS_MESSAGE_CENTER_SETTINGS_BUTTON_LABEL" desc="The button label for visiting the appropriate settings page in the footer of the message center.">
         Settings
       </message>
       <if expr="is_macosx">
         <message name="IDS_MESSAGE_CENTER_SETTINGS_GO_BACK_BUTTON_TOOLTIP" desc="The tooltip on back button that returns from settings to the notification list.">
           Go back to notifications
         </message>
       </if>
       <message name="IDS_MESSAGE_CENTER_SETTINGS_DIALOG_DESCRIPTION" desc="The label to describe the settings dialog.">
         Allow notifications from the following:
@@ skipping 77 matching lines @@
       </message>
       <message name="IDS_APP_LIST_SPEECH_HINT_TEXT" desc="The text label in the speech recognition UI to ask the user to speak the search query">
         Speak now
       </message>
       <message name="IDS_APP_LIST_SPEECH_NETWORK_ERROR_HINT_TEXT" desc="The text label in the speech recognition UI to show the speech recognition can't start because of network error.">
         No internet connection
       </message>
     </messages>
   </release>
 </grit>