SF: VSyncReactor add timestamp querying functions

Adds 2 more functions from the DispSync interface to VSyncReactor,
computeNextRefresh, and expectedPresentTime

Bug: 140303479
Test: 3 new units

Change-Id: I75ea79ed749f05daf3337ddc8ca145e2ecceabcd
diff --git a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
index 82950b5..82b1051 100644
--- a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
@@ -39,6 +39,7 @@
 
     MOCK_METHOD1(addVsyncTimestamp, void(nsecs_t));
     MOCK_CONST_METHOD1(nextAnticipatedVSyncTimeFrom, nsecs_t(nsecs_t));
+    MOCK_CONST_METHOD0(currentPeriod, nsecs_t());
 
     nsecs_t nextVSyncTime(nsecs_t timePoint) const {
         if (timePoint % mPeriod == 0) {