Changes

import com.google.firebase.perf.metrics.AddTrace;

import com.google.firebase.perf.metrics.Trace;

To start a trace, an instance of the Trace class needs to be created via a call to the newTrace() method of the FirebasePerformance instance, passing through the name by which the trace is to be identified. The trace is then started via a call to the start() method of the Trace object: