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.cpp b/cmds/statsd/src/HashableDimensionKey.cpp
index 1502a00..cc706313 100644
--- a/cmds/statsd/src/HashableDimensionKey.cpp
+++ b/cmds/statsd/src/HashableDimensionKey.cpp
@@ -166,10 +166,11 @@
     }
 }
 
-void getDimensionForCondition(const LogEvent& event, Metric2Condition links,
+void getDimensionForCondition(const std::vector<FieldValue>& eventValues,
+                              const Metric2Condition& links,
                               vector<HashableDimensionKey>* conditionDimension) {
     // Get the dimension first by using dimension from what.
-    filterValues(links.metricFields, event.getValues(), conditionDimension);
+    filterValues(links.metricFields, eventValues, conditionDimension);
 
     // Then replace the field with the dimension from condition.
     for (auto& dim : *conditionDimension) {