reduce code

Author: leotianlizhan

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

@@ -383,7 +383,7 @@ private void logAppStartTrace() {
 
   @Override
   public void onActivityPaused(Activity activity) {
-    if (this.firstDrawDone != null && this.preDraw != null) {
+    if (isExperimentTraceDone()) {
       return;
     }
     Timer onPauseTime = clock.getTime();
@@ -397,7 +397,7 @@ public void onActivityPaused(Activity activity) {
 
   @Override
   public void onActivityStopped(Activity activity) {
-    if (this.firstDrawDone != null && this.preDraw != null) {
+    if (isExperimentTraceDone()) {
       return;
     }
     Timer onStopTime = clock.getTime();