Make helpful announcement when there's no focus

chrome/browser/resources/chromeos/chromevox/strings/chromevox_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <grit base_dir="." current_release="1" latest_public_release="0"
       output_all_resource_defines="false" enc_check="möl" source_lang_id="en">
   <outputs>
     <output filename="_locales/am/messages.json" type="chrome_messages_json" lang="am"/>
     <output filename="_locales/ar/messages.json" type="chrome_messages_json" lang="ar"/>
     <output filename="_locales/bg/messages.json" type="chrome_messages_json" lang="bg"/>
     <output filename="_locales/bn/messages.json" type="chrome_messages_json" lang="bn"/>
     <output filename="_locales/ca/messages.json" type="chrome_messages_json" lang="ca"/>
@@ skipping 2657 matching lines @@
       </message>
       <message desc="Describes an audio clip that gets played for a specific event or control type. Use the default string as a guide to what the audio clip represents or conveys." name="IDS_CHROMEVOX_POP_UP_BUTTON_EARCON_DESCRIPTION">
         A pop up button
       </message>
       <message desc="Describes an audio clip that gets played for a specific event or control type. Use the default string as a guide to what the audio clip represents or conveys." name="IDS_CHROMEVOX_SLIDER_EARCON_DESCRIPTION">
         A slider
       </message>
       <message desc="Describes an audio clip that gets played for a specific event or control type. Use the default string as a guide to what the audio clip represents or conveys." name="IDS_CHROMEVOX_WRAP_EARCON_DESCRIPTION">
         Wrap from beginning to end or end to beginning inside of a page, dialog, or other container
       </message>
+      <message desc="Announced when ChromeVox has no item in focus." name="IDS_CHROMEVOX_NO_FOCUS">
+        No focus. Press Control N to open a new window.
+      </message>
     </messages>
   </release>
 </grit>