Issue 3687 - Add experimental support for Safari content blockers

safari/contentBlocking.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
@@ skipping 63 matching lines @@
     // JSON string it fails. Worse still it actually performs the callback twice
     // too, firstly with an empty string and then with an Error:
     //   "Extension compilation failed: Failed to parse the JSON String."
     // To mitigate this we convert the rules to JSON here and also ignore
     // callback values of "". (Usually the callback is performed with either
     // null for success or an Error on failure.)
     // Bug #26322821 filed on bugreport.apple.com
     JSON.stringify(contentBlockerList.generateRules()),
     function(error)
     {
-      if (error === "")

[Sebastian Noack, 2016/05/18 08:13:37]

We always use == unless it makes a difference, as per Mozilla's coding
practices.

[kzar, 2016/05/18 09:28:47]

I wrongly thought that `(new Error("")).toString()` would result in an empty
string but actually it gives "Error". So I guess you're right that this can
never make a difference. Done.

[Sebastian Noack, 2016/05/18 10:07:24]

Even if error.toString() returns "", error == "" would still be false if error
is an object.

[Sebastian Noack, 2016/05/18 10:11:45]

Never mind, you are actually right that == calls the toString() method of
objects. But yeah in the case here it still doesn't matter.

+      if (error == "")
         return;
 
       lastSetContentBlockerError = error;
       callback(error);
     }
   );
 }
 
 function updateContentBlocker(isStartup, legacyAPISupported)
 {
@@ skipping 58 matching lines @@
     });
   });
 }
 
 port.on("safari.contentBlockingActive", (msg, sender) =>
 {
   if (!contentBlockingActive && afterContentBlockingFinished)
     return afterContentBlockingFinished;
   return contentBlockingActive;
 });