Track the number of buckets dropped.

Test: atest statsd_test
Change-Id: I56973d2c87aaed0f1c4a6908682cc54cda39eceb
diff --git a/cmds/statsd/src/metrics/EventMetricProducer.cpp b/cmds/statsd/src/metrics/EventMetricProducer.cpp
index c53c4ce..7e695a6 100644
--- a/cmds/statsd/src/metrics/EventMetricProducer.cpp
+++ b/cmds/statsd/src/metrics/EventMetricProducer.cpp
@@ -77,6 +77,7 @@
 
 void EventMetricProducer::dropDataLocked(const int64_t dropTimeNs) {
     mProto->clear();
+    StatsdStats::getInstance().noteBucketDropped(mMetricId);
 }
 
 void EventMetricProducer::onSlicedConditionMayChangeLocked(bool overallCondition,