pullers now cache data to throttle frequent pull requests.
all pullers have a default 1s cool down before next pull.
We can adjust these later.
Also add puller stats in StatsdStats

Test: unit test
Change-Id: I71894a24c41e059d841591312dbb852f54387b7d
diff --git a/cmds/statsd/src/stats_log.proto b/cmds/statsd/src/stats_log.proto
index ae69a50..2596a5f 100644
--- a/cmds/statsd/src/stats_log.proto
+++ b/cmds/statsd/src/stats_log.proto
@@ -246,4 +246,12 @@
         optional int32 alarms_registered = 1;
     }
     optional AnomalyAlarmStats anomaly_alarm_stats = 9;
+
+    message PulledAtomStats {
+        optional int32 atom_id = 1;
+        optional int64 total_pull = 2;
+        optional int64 total_pull_from_cache = 3;
+        optional int64 min_pull_interval_sec = 4;
+    }
+    repeated PulledAtomStats pulled_atom_stats = 10;
 }
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