Chrome Version       : 63.0.3239.132
OS Version: OS X 10.12.6

What steps will reproduce the problem?
1. just try to add debugger on your javascript code and try refreshing many times, again, and again until it happens and never stops until you have to close the tab and open a new one and start debugging again until sometimes it happens since the first time.

What is the expected result?
I would expect to have the screen to read the code clear and debugeable with easy and grace

What happens instead of that?
it happens this which is SUPER annoying while developing and debugging => https://github.com/google/WebFundamentals/issues/5299


Please provide any additional information below. Attach a screenshot if
possible.

I'm attaching screenshots on this issue Please take a look should not take more than one click and see the issue reported :) Thank you! https://github.com/google/WebFundamentals/issues/5299

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