Issue 491 - Validate custom filters

block.js

Index: block.js
===================================================================
--- a/block.js
+++ b/block.js
@@ -68,8 +68,21 @@
   var filters = document.getElementById("filters").value.split(/[\r\n]+/)
                         .map(function(f) {return f.replace(/^\s+/, "").replace(/\s+$/, "");})
                         .filter(function(f) {return f != "";});
-  ext.backgroundPage.sendMessage({type: "add-filters", filters: filters});
-  closeDialog(true);
+
+  ext.backgroundPage.sendMessage(
+    {
+      type: "add-filters",
+      filters: filters
+    },
+
+    function(response)
+    {
+      if (response.status == "ok")
+        closeDialog(true);
+      else
+        alert(response.error);

[Wladimir Palant, 2014/11/18 16:35:03]

I don't think this message is helpful without indicating which filter it applies
to. Besides, showing the browser's error message in addition to our generic
description would be nice.

[Sebastian Noack, 2014/11/18 17:42:55]

I decided to keep things as simple as possible for now, since we are probably
going to rework the UI anyway. And at the moment any error message is better
than no error message.

Also the browser's error message is as generic as our error message, at least on
Chrome and Safari, though it mentions the selector. However, for other cases of
InvalidFilter there won't even be a browser error.

But I guess we can add the line number at least.

+    }
+  );
 }
 
 function closeDialog(success)