Add missing static imports.

Author: visumickey

firebase-perf/src/main/java/com/google/firebase/perf/metrics/Trace.java

@@ -15,6 +15,8 @@
 package com.google.firebase.perf.metrics;
 
 import static com.google.firebase.perf.metrics.validator.PerfMetricValidator.validateAttribute;
+import static com.google.firebase.perf.metrics.validator.PerfMetricValidator.validateMetricName;
+import static com.google.firebase.perf.metrics.validator.PerfMetricValidator.validateTraceName;
 
 import android.os.Parcel;
 import android.os.Parcelable;