Issue 5098 - Expose FilterStorage initialization state

lib/filterStorage.js

Index: lib/filterStorage.js
===================================================================
--- a/lib/filterStorage.js
+++ b/lib/filterStorage.js
@@ -42,16 +42,22 @@ let formatVersion = 4;
 /**
  * This class reads user's filters from disk, manages them in memory
  * and writes them back.
  * @class
  */
 let FilterStorage = exports.FilterStorage =
 {
   /**
+   * Will be set to true after the initial loadFromDisk() call completes.
+   * @type {boolean}
+   */
+  initialized: false,
+
+  /**
    * Version number of the patterns.ini format used.
    * @type {number}
    */
   get formatVersion()
   {
     return formatVersion;
   },
 
@@ -458,16 +464,18 @@ let FilterStorage = exports.FilterStorag
   {
     let readFile = () =>
     {
       let parser = {
         process: this.importData()
       };
       IO.readFromFile(this.sourceFile, parser, readFromFileException =>
       {
+        this.initialized = true;
+
         if (!readFromFileException && this.subscriptions.length == 0)
         {
           // No filter subscriptions in the file, this isn't right.
           readFromFileException = new Error("No data in the file");
         }
 
         if (readFromFileException)
           Cu.reportError(readFromFileException);
@@ -489,16 +497,17 @@ let FilterStorage = exports.FilterStorag
       });
     };
 
     IO.statFile(this.sourceFile, (statError, statData) =>
     {
       if (statError || !statData.exists)
       {
         this.firstRun = true;
+        this.initialized = true;
         FilterNotifier.triggerListeners("load");
       }
       else
         readFile();
     });
   },
 
   /**