Fixed problem introduced in previous pull request.

Very sorry but there was a bug in my previous pull request! I have tested this fix and hopefully now it should be working fully. 

The updateRecord and helper functions I added in the previous pull request were incorrectly just functions and not member functions, this resulted in "this" being unbound when _updateRecords called its own helper functions even though _updateRecords itself was explicitly bound to the correct this. They have been moved into the ChromeStorage object as members functions which should fix this problem.