add feature: GaugeMetricProducer now takes repeated list of fields
bug fix: GaugeMetricProducer now works better with pulled events.
unit test also includes GaugeMetricProducer_test

Test: unit test
Change-Id: Ic60f09342d14cfb107be2130d445b323a56909e0
diff --git a/cmds/statsd/src/stats_util.cpp b/cmds/statsd/src/stats_util.cpp
index bfa3254..7527a64 100644
--- a/cmds/statsd/src/stats_util.cpp
+++ b/cmds/statsd/src/stats_util.cpp
@@ -35,6 +35,9 @@
             case KeyValuePair::ValueCase::kValueInt:
                 flattened += std::to_string(pair.value_int());
                 break;
+            case KeyValuePair::ValueCase::kValueLong:
+                flattened += std::to_string(pair.value_long());
+                break;
             case KeyValuePair::ValueCase::kValueBool:
                 flattened += std::to_string(pair.value_bool());
                 break;