Duration tracker optimization.

* Avoid querying sliced condition for stop/stopAll events for duration metric.
* Avoid extracting the internal dimension key when it is identical to the what dimension.

Test: statsd test
Change-Id: I664e8d3b1a68960d05c9ce4789caefb60b1ab502
diff --git a/cmds/statsd/src/HashableDimensionKey.h b/cmds/statsd/src/HashableDimensionKey.h
index 5d016e9..57bdf68 100644
--- a/cmds/statsd/src/HashableDimensionKey.h
+++ b/cmds/statsd/src/HashableDimensionKey.h
@@ -144,7 +144,8 @@
 void filterGaugeValues(const std::vector<Matcher>& matchers, const std::vector<FieldValue>& values,
                        std::vector<FieldValue>* output);
 
-void getDimensionForCondition(const LogEvent& event, Metric2Condition links,
+void getDimensionForCondition(const std::vector<FieldValue>& eventValues,
+                              const Metric2Condition& links,
                               std::vector<HashableDimensionKey>* conditionDimension);
 
 }  // namespace statsd