Issue 5146 - Implement DownloadableSubscription parsing in C++

compiled/StringScanner.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 23 matching lines @@
   bool done() const
   {
     return mPos >= mEnd;
   }
 
   String::size_type position() const
   {
     return mPos - 1;
   }
 
+  void back()
+  {
+    if (mPos > 0)
+      mPos--;
+  }
+
   String::value_type next()
   {
     String::value_type result = done() ? mTerminator : mStr[mPos];
     mPos++;
     return result;
   }
 
   bool skipOne(String::value_type ch)
   {
     if (!done() && mStr[mPos] == ch)
     {
       mPos++;
       return true;
     }
 
     return false;
   }
 
   bool skip(String::value_type ch)
   {
     bool skipped = false;
     while ((skipped = skipOne(ch)));
     return skipped;
   }
 };