Issue 4579 - Fix ESLint errors

polyfill.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 112 matching lines @@
         });
       });
     };
 
     Object.defineProperty(object, name, descriptor);
   }
 
   function wrapRuntimeOnMessage()
   {
     let {onMessage} = browser.runtime;
-    let {addListener, removeListener, hasListener} = onMessage;
+    let {addListener, removeListener} = onMessage;
 
     onMessage.addListener = function(listener)
     {
       if (typeof listener != "function")
         throw new Error(invalidMessageListenerError);
 
       // Don't add the same listener twice or we end up with multiple wrappers.
       if (messageListeners.has(listener))
         return;
 
       let wrapper = (message, sender, sendResponse) =>
       {
         let wait = listener(message, sender, sendResponse);
 
         if (wait instanceof Promise)
         {
           wait.then(sendResponse, reason =>
           {
             try
             {
               sendResponse();
             }
-            finally
+            catch (error)
             {
               // sendResponse can throw if the internal port is closed; be sure
               // to throw the original error.
-              throw reason;
             }
+
+            throw reason;
           });
         }
 
         return !!wait;
       };
 
       addListener.call(onMessage, wrapper);
       messageListeners.set(listener, wrapper);
     };
 
@@ skipping 48 matching lines @@
 
   // Workaround since HTMLCollection, NodeList, StyleSheetList, and CSSRuleList
   // didn't have iterator support before Chrome 51.
   // https://bugs.chromium.org/p/chromium/issues/detail?id=401699
   for (let object of [HTMLCollection, NodeList, StyleSheetList, CSSRuleList])
   {
     if (!(Symbol.iterator in object.prototype))
       object.prototype[Symbol.iterator] = Array.prototype[Symbol.iterator];
   }
 }