SF: Adding Mock Display and tests for RefreshRateStats.

Following ag/6005545.

Test: adding SF tests.
Bug: 113612090
Change-Id: Ic4d1ca622f00c4396ae19c44defac0c69fabed1d
diff --git a/services/surfaceflinger/Scheduler/RefreshRateStats.h b/services/surfaceflinger/Scheduler/RefreshRateStats.h
index cd81e4d..7e22232 100644
--- a/services/surfaceflinger/Scheduler/RefreshRateStats.h
+++ b/services/surfaceflinger/Scheduler/RefreshRateStats.h
@@ -82,9 +82,11 @@
 
         std::unordered_map<std::string, int64_t> totalTime;
         for (auto config : mRefreshRateConfigs->getRefreshRates()) {
+            int64_t totalTimeForConfig = 0;
             if (mConfigModesTotalTime.find(config.configId) != mConfigModesTotalTime.end()) {
-                totalTime[config.name] = mConfigModesTotalTime.at(config.configId);
+                totalTimeForConfig = mConfigModesTotalTime.at(config.configId);
             }
+            totalTime[config.name] = totalTimeForConfig;
         }
         return totalTime;
     }