Support dimension in condition in metric producers.

Test: added e2e tests for count/duration metrics sliced by fields in condition and with/without links.

Change-Id: Ie34deba68e6780abdde458be3f0ce5284e76a1a2
diff --git a/bin/src/stats_util.h b/bin/src/stats_util.h
index 160b1f4..31f51a7 100644
--- a/bin/src/stats_util.h
+++ b/bin/src/stats_util.h
@@ -28,13 +28,14 @@
 namespace statsd {
 
 const HashableDimensionKey DEFAULT_DIMENSION_KEY = HashableDimensionKey();
+const MetricDimensionKey DEFAULT_METRIC_DIMENSION_KEY = MetricDimensionKey();
 
 // Minimum bucket size in seconds
 const long kMinBucketSizeSec = 5 * 60;
 
 typedef std::map<int64_t, std::vector<HashableDimensionKey>> ConditionKey;
 
-typedef std::unordered_map<HashableDimensionKey, int64_t> DimToValMap;
+typedef std::unordered_map<MetricDimensionKey, int64_t> DimToValMap;
 
 }  // namespace statsd
 }  // namespace os