SF: VSyncReactor add period modification functions

Adds 2 more functions from the DispSync interface to VSyncReactor,
{get,set}Period

Bug: 140303479
Test: 2 new units

Change-Id: Ie0084597c80d6d43099201fb49b71ae9badea3ee
diff --git a/services/surfaceflinger/tests/unittests/VSyncDispatchRealtimeTest.cpp b/services/surfaceflinger/tests/unittests/VSyncDispatchRealtimeTest.cpp
index 448954f..484947d 100644
--- a/services/surfaceflinger/tests/unittests/VSyncDispatchRealtimeTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncDispatchRealtimeTest.cpp
@@ -49,6 +49,8 @@
 
     nsecs_t currentPeriod() const final { return mPeriod; }
 
+    void setPeriod(nsecs_t) final {}
+
 private:
     nsecs_t const mPeriod;
 };
@@ -80,6 +82,8 @@
         return mPeriod;
     }
 
+    void setPeriod(nsecs_t) final {}
+
 private:
     std::mutex mutable mMutex;
     nsecs_t mPeriod;