Performance Changes from UMA Sampling Profiler

In summer 2017, Predator was extended to analyze performance regressions and improvements detected by the UMA Sampling Profiler. This component is fully functional and work is in progress to start surfacing some of its analyses in:

1. Email alerts to CL authors. These will inform an author if their CL has been identified as causing a performance regression or improvement. This will help provide more high-quality feedback to engineers about the performance impact of their changes on real users.
2. The UMA Sampling Profiler dashboard. This will assist engineers who are proactively investigating performance regressions by pointing them to likely culprits.