Issue 4494 - Avoid causing some sandbox related warnings

inject.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 371 matching lines @@
   if ("RTCPeerConnection" in window)
     window.RTCPeerConnection = boundWrappedRTCPeerConnection;
   if ("webkitRTCPeerConnection" in window)
     window.webkitRTCPeerConnection = boundWrappedRTCPeerConnection;
 }
 
 if (document instanceof HTMLDocument)
 {
   let sandbox = window.frameElement &&
                 window.frameElement.getAttribute("sandbox");
-  if (typeof sandbox != "string" || sandbox.includes("allow-scripts"))
+
+  if (typeof sandbox != "string" || /(^|\s)allow-scripts(\s|$)/i.test(sandbox))
   {
     let script = document.createElement("script");
     script.type = "application/javascript";
     script.async = false;
     script.textContent = "(" + injected + ")('" + randomEventName + "');";
     document.documentElement.appendChild(script);
     document.documentElement.removeChild(script);
   }
 }