Always report the metric id even if the metric has no data to upload.

This is to normalize the metric when applying cross-device aggregation.

Test: statsd test
BUG: b/118203108

Change-Id: I644a6a4163e2d2ad8f70e0c4e002dd4f542248af
diff --git a/cmds/statsd/src/stats_log.proto b/cmds/statsd/src/stats_log.proto
index 32ee5af..a6f27c8 100644
--- a/cmds/statsd/src/stats_log.proto
+++ b/cmds/statsd/src/stats_log.proto
@@ -219,6 +219,8 @@
   optional DimensionsValue dimensions_path_in_what = 11;
 
   optional DimensionsValue dimensions_path_in_condition = 12;
+
+  optional bool is_active = 13;
 }
 
 message UidMapping {