Provide a warning or property to handle 150 request resource limit of Performance API

[bradgreens]

This improves debugging in relation to my issue where the Performance API exceeded 150 entries and produced errors.

If there are 150 performance entries and the Network JS latency request is not one of them, the script will fail. This could be handled gracefully by providing the user a warning and/or by adding a flag to Network JS to flush performance entries prior to executing the latency test.

PR opened

note: I realize 150 requests is way too many. If anyone wonders what the use case is, it's an angular app in the development environment, and without concatenation 400 requests is not uncommon.