UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36

Steps to reproduce the problem:
This is an extremely strange bug. I spent 2 days trying to narrow it down.

In a complex javascript application I have the following method:

        SheetItem.prototype.markChanged = function () {
            // aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
            // aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
            if (!this.trackChanges) {
                return;
            }
            //var status = ItemStatus.Intact;
            //if (status === ItemStatus.Intact)
            //{
            //    //this.status(ItemStatus.Changed);
            if (this.status.peek() === ItemStatus.Intact) {
                this.status(ItemStatus.Changed);
            }
        };

It does not do anything and still takes 20ms to complete, so it hangs the system when called 10 000 times. If I just add another character at the end of the first comment, e.g. 'B':

        SheetItem.prototype.markChanged = function () {
            // aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaB
            // aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
            if (!this.trackChanges) {
                return;
            }
            //var status = ItemStatus.Intact;
            //if (status === ItemStatus.Intact)
            //{
            //    //this.status(ItemStatus.Changed);
            if (this.status.peek() === ItemStatus.Intact) {
                this.status(ItemStatus.Changed);
            }
        };

, it starts working fine. All other subtle changes to the text of the method cause dramatic changes to the timing as well. It makes 2 calls to other methods, but I had a version that would take 20ms to run without any external calls.

Also, if I put a breakpoint in the method, run to it and then remove it and press F8, the method starts working fine.

All the above depends on the current context of the application. If I let the operation complete, which takes 3 min (20ms * 10000 = 200 sec), next time I run it, it works fine (the method takes 0ms).

Apparently, it is virtually impossible for you to reproduce the bug without having the whole system in your development environment.

What is the expected behavior?
Adding 1 character to a comment should not change the execution time by million times

What went wrong?
See above

Did this work before? N/A 

Chrome version: 56.0.2924.87  Channel: stable
OS Version: 10.0
Flash Version: