Add support for secure system overlays.  (DO NOT MERGE)

This change adds a new window type for secure system overlays
created by the system itself from non-secure system overlays that
might be created by applications that have the system alert permission.
Secure views ignore the presence of secure system overlays.

Bug: 3098519
Change-Id: I8f8398f4fdeb0469e5d71124c21bedf121bd8c07
diff --git a/include/ui/InputDispatcher.h b/include/ui/InputDispatcher.h
index 3599163..4955d47 100644
--- a/include/ui/InputDispatcher.h
+++ b/include/ui/InputDispatcher.h
@@ -183,6 +183,7 @@
         TYPE_INPUT_METHOD_DIALOG= FIRST_SYSTEM_WINDOW+12,
         TYPE_WALLPAPER          = FIRST_SYSTEM_WINDOW+13,
         TYPE_STATUS_BAR_PANEL   = FIRST_SYSTEM_WINDOW+14,
+        TYPE_SECURE_SYSTEM_OVERLAY = FIRST_SYSTEM_WINDOW+15,
         LAST_SYSTEM_WINDOW      = 2999,
     };