[Chromecast] Don't log time to first paint if no app has been set.

chromecast/base/metrics/cast_metrics_helper.cc

Index: chromecast/base/metrics/cast_metrics_helper.cc
diff --git a/chromecast/base/metrics/cast_metrics_helper.cc b/chromecast/base/metrics/cast_metrics_helper.cc
index 0e0c889894a3f398328ea69ae0b17aabb531eee9..85cdfe8931e8f10a0fdfb920869b7d340a9220bf 100644
--- a/chromecast/base/metrics/cast_metrics_helper.cc
+++ b/chromecast/base/metrics/cast_metrics_helper.cc
@@ -149,6 +149,8 @@ void CastMetricsHelper::LogMediaPause() {
 
 void CastMetricsHelper::LogTimeToFirstPaint() {
   MAKE_SURE_THREAD(LogTimeToFirstPaint);
+  if (app_id_.empty())
+    return;
   base::TimeDelta launch_time = base::TimeTicks::Now() - app_start_time_;
   const std::string uma_name(GetMetricsNameWithAppName("Startup",
                                                        "TimeToFirstPaint"));