Issue 5098 - Expose FilterStorage initialization state

test/filterStorage_readwrite.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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 92 matching lines @@
       return 1;
     return 0;
   });
   return sections.map(
     section => [section.header].concat(section.data).join("\n")
   ).join("\n");
 }
 
 function testReadWrite(test, withExternal)
 {
+  test.ok(!FilterStorage.initialized, "Uninitialized before the first load");
+
   return testData.then(data =>
   {
     dataFile.contents = data;
     return loadFilters();
   }).then(() =>
   {
+    test.ok(FilterStorage.initialized, "Initialize after the first load");
     test.equal(FilterStorage.fileProperties.version, FilterStorage.formatVersion, "File format version");
 
     if (withExternal)
     {
       {
         let subscription = new ExternalSubscription("~external~external subscription ID", "External subscription");
         subscription.filters = [Filter.fromText("foo"), Filter.fromText("bar")];
         FilterStorage.addSubscription(subscription);
       }
 
@@ skipping 192 matching lines @@
     return FilterStorage.restoreBackup(1);
   }).then(() =>
   {
     test.equal(FilterStorage.subscriptions.length, 1, "Subscription count after restoring backup");
     return loadFilters();
   }).then(() =>
   {
     test.equal(FilterStorage.subscriptions.length, 1, "Subscription count after reloading");
   }).catch(unexpectedError.bind(test)).then(() => test.done());
 };