a11y/Mac: Add screenreader support for SubtleNotificationView announcements.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index f9dec2db77a38628b59c52a9fb5e1859f7db4a51..3cd4e0edc39ce288b3658740739be1fc72371387 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -12796,6 +12796,11 @@ Some features may be unavailable.  Please check that the profile exists and you
       </message>
 
       <!-- Backspace shortcut notification strings -->
+      <if expr="is_macosx">
+        <message name="IDS_MAC_COMMAND_KEY_DESCRIPTION" desc="Description for the Mac Command key icon (⌘).">
+          Command
+        </message>
+      </if>
       <message name="IDS_PRESS_ALT_LEFT_TO_GO_BACK" desc="Text displayed in the bubble to explain the keyboard shortcut to go back to the previous web page in history. The accelerators are names of keyboard keys. Please surround the names of the keys (e.g. 'Alt' and '←') in pipe characters so they can be rendered correctly.">
         Press |<ph name="ACCELERATOR1">$1<ex>Alt</ex></ph>|+|<ph name="ACCELERATOR2">$2<ex>←</ex></ph>| to go back
       </message>