Issue 6592 - Implement $rewrite filter option

test/_common.js

Index: test/_common.js
===================================================================
--- a/test/_common.js
+++ b/test/_common.js
@@ -26,19 +26,20 @@
   NS_BINDING_ABORTED: 0x804B0002,
   NS_ERROR_FAILURE: 0x80004005
 };
 
 const MILLIS_IN_SECOND = exports.MILLIS_IN_SECOND = 1000;
 const MILLIS_IN_MINUTE = exports.MILLIS_IN_MINUTE = 60 * MILLIS_IN_SECOND;
 const MILLIS_IN_HOUR = exports.MILLIS_IN_HOUR = 60 * MILLIS_IN_MINUTE;
 
-function URL(urlString)
+// URL is global in Node 10. In Node 7+ it must be imported.

[kzar, 2018/05/16 13:24:31]

(Thanks for noting the versions involved here.)

+if (global.URL == undefined)

[kzar, 2018/05/16 13:24:31]

I wonder why we put it in the global Object here, then from there put it in the
globals Object later. Also don't we normally do something like `typeof foo ==
"undefined"` which checking for undefined?

So I wonder if this would work instead:

let globals = {
  ...
  URL: typeof "URL" == undefined ? require("url").URL : URL;
};

[hub, 2018/05/16 18:33:23]

The previous polyfill was to define `function URL()`. Similarly here we just
import the symbol into the global space. And I think that's the right approach.

Whether we add it to `globals` or not is irrelevant, that part is for the
sandboxing.

BTW `typeof "URL"` is "String" ;-)

[kzar, 2018/05/17 09:49:01]

Well for some longer functions we declare them earlier on in this file (not in
the global space as far as I can tell) and then pass the reference through into
`globals` so that they can be used by the (sandboxed) tests. Some shorter values
/ functions we just inline in the `globals` Object, for example `atob`.
That is the only relevant part surely, it's the part that makes the tests pass.
Sure, sorry that was a typo.

Anyway I've just double checked (Node.js 8) and my suggestion does work. It's
shorter, less confusing (global vs gloals) and doesn't pointlessly declare the
function in the global scope. So without the typo it looks something like this:

let globals = {
  ...
  // URL is global in Node 10. In Node 7+ it must be imported.
  URL: typeof URL == "undefined" ? require("url").URL : URL
};

[hub, 2018/05/17 12:50:46]

I had no doubt this would be working.
Done.

 {
-  return require("url").parse(urlString);
+  global.URL = require("url").URL;
 }
 
 let Services = {
   obs: {
     addObserver() {}
   }
 };
 let XPCOMUtils = {