Feature request: Warn users using metric thresholds

[kevinweber]

How we can provide better guidance to developers who usually don't work on performance? Here's an idea:

• Allow setting a threshold for each metric to educate developers about what’s acceptable (e.g. 50ms for mounting a component)
• If a threshold is exceeded, the metric should clearly stick out (see mockup below)
• Developers should be able to override the default threshold for each metric

Render times and other metrics can change between runs and machines, and so does the performance in the real world! Calculating the rendering time of a component that runs on a development version of React and on a developer machine might be closer to the performance of components running on real world slow devices in production mode.

Therefore, the threshold should be met even on slow machines and when running uncompressed code.

[alexreardon]

Interesting! This would be cool. I think the variance between machines will make it tricky, but keen if you want to have a look into it!