Issue 2325 - Add a way to set settings in libadblockplus for FRP and automatic updates

lib/prefs.js

Index: lib/prefs.js
===================================================================
--- a/lib/prefs.js
+++ b/lib/prefs.js
@@ -41,9 +41,13 @@
   update_hard_expiration: 0,
   currentVersion: "0.0",
   notificationdata: {},
-  notificationurl: "https://notification.adblockplus.org/notification.json"
+  notificationurl: "https://notification.adblockplus.org/notification.json",
+  suppress_first_run_page: false,
+  disable_auto_updates: false
 };
 
+let preconfigurable = ["suppress_first_run_page", "disable_auto_updates"];
+
 let values = Object.create(defaults);
 let path = _fileSystem.resolve("prefs.json");
 let listeners = [];
@@ -75,6 +79,18 @@
 
 function load()
 {
+  // Set default prefs based on _preconfiguredPrefs
+  for (let key in _preconfiguredPrefs)
+  {
+    if (preconfigurable.indexOf(key) != -1)
+    {
+      if (typeof _preconfiguredPrefs[key] != typeof defaults[key])

[Felix Dahlke, 2015/06/12 11:55:35]

Don't think we need to check for this - we don't do it on other platforms
either.

[Oleksandr, 2015/06/12 12:29:59]

Done.

+        throw new Error("Attempt to change preference type through preconfiguration");
+      defaults[key] = _preconfiguredPrefs[key];

[Felix Dahlke, 2015/06/12 11:55:35]

Was about to complain that this isn't necessary, but it actually could be. If we
don't this, we'd be introducing a footgun:

defaults = {x: 1}
preconfiguredPrefs = {x: 2}
Prefs.x = 1;
restoreDefault("x");
Prefs.x == 2; // Nope, it's 1

Now, restoreDefault() doesn't actually exist IIRC, but in Firefox we have it,
and if we add it in libdablockplus as well, our feet are in danger.

But I think we can solve this by simply modifying defaults once, rather than
messing with both defaults and values. In particular:

1. We move this out of load(), where it probably doesn't really belong, and put
it right before the `for (let key in defaults)` loop below. And then we just do
this:

for (let key in _preconfiguredPrefs)
  if (preconfigurable.indexOf(key) != -1)
    defaults[key] = _preconfiguredPrefs[key];

2. We will have to move the initialisation of "values" down there, before the
load() call.

IMHO it's simpler that way. We just modify defaults to begin with, the rest of
the code works the same as before.

[Oleksandr, 2015/06/12 12:29:59]

Done.

+      values[key] = _preconfiguredPrefs[key];
+    }
+  }
+
   _fileSystem.read(path, function(result)
   {
     // prefs.json is expected to be missing, ignore errors reading file