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/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index ad31a40..e34e568 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -44,8 +44,10 @@
         "LayerHistoryTest.cpp",
         "SchedulerTest.cpp",
         "SchedulerUtilsTest.cpp",
+        "RefreshRateStatsTest.cpp",
         "TimeStatsTest.cpp",
         "mock/DisplayHardware/MockComposer.cpp",
+        "mock/DisplayHardware/MockDisplay.cpp",
         "mock/DisplayHardware/MockPowerAdvisor.cpp",
         "mock/gui/MockGraphicBufferConsumer.cpp",
         "mock/gui/MockGraphicBufferProducer.cpp",