MediaMetrics: Add and fix clang-tidy

Test: adb shell dumpsys media.metrics
Test: atest mediametrics_tests
Bug: 149850236
Change-Id: Ia02fad2cbefdbfe3deba3897526a21dd88270c27
diff --git a/services/mediametrics/statsd_audiotrack.cpp b/services/mediametrics/statsd_audiotrack.cpp
index 397cdf3..ee5b9b2 100644
--- a/services/mediametrics/statsd_audiotrack.cpp
+++ b/services/mediametrics/statsd_audiotrack.cpp
@@ -39,7 +39,7 @@
 
 bool statsd_audiotrack(const mediametrics::Item *item)
 {
-    if (item == NULL) return false;
+    if (item == nullptr) return false;
 
     // these go into the statsd wrapper
     const nsecs_t timestamp = MediaMetricsService::roundTime(item->getTimestamp());
@@ -146,4 +146,4 @@
     return true;
 }
 
-};
+} // namespace android