Document that navigator.appName is always "Netscape" (per spec)

Source/core/frame/NavigatorID.idl

 /*
  * Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://html.spec.whatwg.org/#client-identification
 
 [
     NoInterfaceObject, // Always used on target of 'implements'
     Exposed=(Window,Worker),
 ] interface NavigatorID {
     readonly attribute DOMString appCodeName; // constant "Mozilla"
-    readonly attribute DOMString appName;
+    readonly attribute DOMString appName; // constant "Netscape"
     readonly attribute DOMString appVersion;
     readonly attribute DOMString platform;
     readonly attribute DOMString product; // constant "Gecko"
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=22555
     // boolean taintEnabled(); // constant false
     readonly attribute DOMString userAgent;
 };