SF: VSyncTracker, clear timestamps on beginResync

DispSync would clear its internal model around power events, as the
vsync timings during power mode changes are not accurate for screen-on
vsync prediction. DispSync uses the beginResync signal for this, and the
new system does the same (although once DispSync is deprecated,
begin/endResync should go away too).

Fixes: 146050690
Test: Dogfooding blueline
Test: 2 new unit tests
Change-Id: Ie4b607029516dcea0e5d65afca75a7017bf63e12
diff --git a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
index 5aff429..b23159b 100644
--- a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
@@ -41,6 +41,7 @@
     MOCK_CONST_METHOD1(nextAnticipatedVSyncTimeFrom, nsecs_t(nsecs_t));
     MOCK_CONST_METHOD0(currentPeriod, nsecs_t());
     MOCK_METHOD1(setPeriod, void(nsecs_t));
+    MOCK_METHOD0(resetModel, void());
 
     nsecs_t nextVSyncTime(nsecs_t timePoint) const {
         if (timePoint % mPeriod == 0) {