Issue 5028 - Use browser namespace

lib/io.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 45 matching lines @@
     );
   });
 }
 
 function removeFile(fileName)
 {
   return new Promise((resolve, reject) =>
   {
     ext.storage.remove(fileToKey(fileName), () =>
     {
-      if (chrome.runtime.lastError)
-        reject(chrome.runtime.lastError.message);
+      if (browser.runtime.lastError)
+        reject(browser.runtime.lastError.message);
       else
         resolve();
     });
   });
 }
 
 exports.IO =
 {
   /**
    * Reads text lines from a file.
@@ skipping 52 matching lines @@
    *    Promise to be resolved or rejected once the operation is completed
    */
   renameFile(fromFile, newName)
   {
     return loadFile(fromFile).then(entry =>
     {
       return new Promise((resolve, reject) =>
       {
         ext.storage.set(fileToKey(newName), entry, () =>
         {
-          if (chrome.runtime.lastError)
-            reject(chrome.runtime.lastError.message);
+          if (browser.runtime.lastError)
+            reject(browser.runtime.lastError.message);
           else
             resolve();
         });
       });
     }).then(() => removeFile(fromFile));
   },
 
   /**
    * Removes a file.
    * @param {string} fileName
@@ skipping 23 matching lines @@
         lastModified: entry.lastModified
       };
     }).catch(error =>
     {
       if (error.type == "NoSuchFile")
         return {exists: false};
       throw error;
     });
   }
 };