Statsd guardrail for Alerts

Now, each config is allowed at most 100 Alerts in it.
That is, for each uid, for each config id, the config's alert section
can have at most 100 items in it.

Bug: 73287046
Test: none yet
Change-Id: I2c81bc647627e432337c359c0a76aa3fc08bdd23
diff --git a/cmds/statsd/src/metrics/MetricProducer.h b/cmds/statsd/src/metrics/MetricProducer.h
index e8f8299..4ee9471 100644
--- a/cmds/statsd/src/metrics/MetricProducer.h
+++ b/cmds/statsd/src/metrics/MetricProducer.h
@@ -123,6 +123,7 @@
         return byteSizeLocked();
     }
 
+    /* If alert is valid, adds an AnomalyTracker and returns it. If invalid, returns nullptr. */
     virtual sp<AnomalyTracker> addAnomalyTracker(const Alert &alert) {
         std::lock_guard<std::mutex> lock(mMutex);
         sp<AnomalyTracker> anomalyTracker = new AnomalyTracker(alert, mConfigKey);