Chrome developer tools do not show all JavaScript files any more

For me I just had to open the Developer Tools settings and click on the "Restore defaults and reload" button in the first tab.

Then all my local scripts showed up again and debugging was back to normal.

Add the debugger; instruction at any part of your script, the debugger will stop at this point and show you the script, even if the script is dynamically loaded.

                onSuccess: function (result) {
                    debugger;
                    combo.empty();
                    $(result).each(function () {
                        var option;

                        option = document.createElement('option');
                        option.value = this.Id;

                        $(option).appendTo(combo);
                    });
                }

Opened the network tab in developer tools and pressed F5 to refresh - thanks @Seano666 for your comment on the question