SF: hwvsync on for more samples on recalibration

Decrease the amount of time that the VSyncPredictor is using the
idealPeriod (ie, the hwc-reported period) by leaving hwVsync on until
there's enough info (4 additional pulses) to infer device's
measured/actual period.

This will benefit frames that come intermittently, as the vsync's
cumulative error over the larger time gap will be smaller, giving the
timer a better chance of landing closer to the vsync signal when those
one-off frames come in.

Test: 3 new unit tests, 2 other tests modified in substance.
Test: dogfooding
Test: uibench
Fixes: 159896971

Change-Id: Ic3190822e38c5a24d3445ea89ef6d7e34a590077
Merged-In: Ic3190822e38c5a24d3445ea89ef6d7e34a590077
(cherry picked from commit b818bfaf7b5bb2f62ed8af0a3ede300a8eb65e2f)
diff --git a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
index d940dc5..65c391d 100644
--- a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
@@ -47,6 +47,7 @@
     MOCK_CONST_METHOD0(currentPeriod, nsecs_t());
     MOCK_METHOD1(setPeriod, void(nsecs_t));
     MOCK_METHOD0(resetModel, void());
+    MOCK_CONST_METHOD0(needsMoreSamples, bool());
     MOCK_CONST_METHOD1(dump, void(std::string&));
 
     nsecs_t nextVSyncTime(nsecs_t timePoint) const {