Issue 4795 - Use modern JavaScript syntax

lib/csp.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 let {defaultMatcher} = require("matcher");
 let {BlockingFilter, RegExpFilter} = require("filterClasses");
 let {getDecodedHostname} = require("url");
 
-chrome.webRequest.onHeadersReceived.addListener(function(details)
+chrome.webRequest.onHeadersReceived.addListener(details =>
 {
   let hostname = getDecodedHostname(new URL(details.url));
   let match = defaultMatcher.matchesAny("", RegExpFilter.typeMap.WEBSOCKET,
                                         hostname, false, null, true);
   if (match instanceof BlockingFilter)
   {
     details.responseHeaders.push({
       name: "Content-Security-Policy",
       // We're blocking WebSockets here by adding a connect-src restriction
       // since the Chrome extension API does not allow us to intercept them.
       // https://bugs.chromium.org/p/chromium/issues/detail?id=129353
       //
       // We also need the child-src and object-src restrictions since CSPs are
       // not inherited from the parent for documents with data: and blob: URLs.
       // https://bugs.chromium.org/p/chromium/issues/detail?id=513860
       //
       // "http:" also includes "https:" implictly.
       // https://www.chromestatus.com/feature/6653486812889088
       value: "connect-src http:; child-src http:; object-src http:"
     });
     return {responseHeaders: details.responseHeaders};
   }
 }, {
   urls: ["http://*/*", "https://*/*"],
   types: ["main_frame", "sub_frame"]
 }, ["blocking", "responseHeaders"]);