Fix accessability for web notification tray.

ash/ash_strings.grd

Index: ash/ash_strings.grd
diff --git a/ash/ash_strings.grd b/ash/ash_strings.grd
index e4561904ea32650fa3d882faa0311a3804a6531e..336401487e620992ca3e66bf101f0eddf4600cf3 100644
--- a/ash/ash_strings.grd
+++ b/ash/ash_strings.grd
@@ -443,6 +443,9 @@ Press Search key to cancel.
       <message name="IDS_ASH_WEB_NOTFICATION_TRAY_NO_MESSAGES" desc="The message displayed in the message center when there are no notifications.">
         You have no notifications. Relax!
       </message>
+      <message name="IDS_ASH_WEB_NOTIFICATION_TRAY_ACCESSIBLE_NAME" desc="The accessible name of the web notification tray (message center).">
+        Message Center
+      </message>
       <message name="IDS_ASH_MAXIMIZE_WINDOW" desc="A help text to show that when the button gets clicked the window get maximized.">
         Maximize
       </message>