[Android] Add accessibility announcement when switching tab models

chrome/android/java/strings/android_chrome_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- android_chrome_strings.grd contains strings for Chrome for Android.
 
 FAQ:
   - How do I add, change, or remove a string?
       Just update this file.
   - Translations will happen automatically??
       Yes, indeed. Just add your string before the branch point and
       make the description good.
@@ skipping 1284 matching lines @@
         Please wait…
       </message>
 
       <!-- Tab switcher -->
       <message name="IDS_ACCESSIBILITY_TAB_SWITCHER_STANDARD_STACK" desc="Content description for the standard stack selection 'button'.">
         Standard tabs
       </message>
       <message name="IDS_ACCESSIBILITY_TAB_SWITCHER_INCOGNITO_STACK" desc="Content description for the incognito stack selection 'button'.">
         Incognito tabs
       </message>
+      <message name="IDS_ACCESSIBILITY_TAB_SWITCHER_STANDARD_STACK_SELECTED" desc="Announcement when the standard tab stack is selected.">
+        Switched to standard tabs
+      </message>
+      <message name="IDS_ACCESSIBILITY_TAB_SWITCHER_INCOGNITO_STACK_SELECTED" desc="Announcement when the incognito tab stack is selected.">
+        Switched to incognito tabs
+      </message>
       <message name="IDS_ACCESSIBILITY_TAB_SWITCHER_UNDO_TAB_CLOSED" desc="Content description for the undo tab closed 'button.">
         Reopen closed tab
       </message>
       <message name="IDS_ACCESSIBILITY_TABSTRIP_TAB" desc="Content description for the tab title.">
         <ph name="TAB_TITLE">%1$s<ex>Welcome to Facebook</ex></ph>, tab
       </message>
       <message name="IDS_ACCESSIBILITY_TABSTRIP_BTN_CLOSE_TAB" desc="Content description for the close tab button.">
         Close tab
       </message>
       <message name="IDS_TAB_LOADING_DEFAULT_TITLE" desc="The title of a tab when we are still waiting for either the URL or the real title. This generally shows when the page is first loading.">
@@ skipping 1389 matching lines @@
         Tap this button for quick access to your tabs.
       </message>
 
       <!-- Item Chooser UI strings -->
       <message name="IDS_ITEM_CHOOSER_ITEM_NAME_WITH_ID" desc="To distinguish items with the same name, the item chooser shows the item name with id.">
         <ph name="ITEM_NAME">%1$s<ex>item_name</ex></ph> (<ph name="ITEM_ID">%2$s<ex>item id</ex></ph>)
       </message>
     </messages>
   </release>
 </grit>