SF: ignore very close vsync timestamps

Check for very close vsync timestamps and mark those
as invalid.

Test: SF unit tests
Bug: 190331974
Change-Id: I13ccc09d6a07847fdfc60242a1a65246fa9674ac
diff --git a/services/surfaceflinger/Scheduler/VSyncPredictor.cpp b/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
index 329e4a0..e9bd92a 100644
--- a/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
+++ b/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
@@ -69,7 +69,21 @@
 
     auto const aValidTimestamp = mTimestamps[mLastTimestampIndex];
     auto const percent = (timestamp - aValidTimestamp) % mIdealPeriod * kMaxPercent / mIdealPeriod;
-    return percent < kOutlierTolerancePercent || percent > (kMaxPercent - kOutlierTolerancePercent);
+    if (percent >= kOutlierTolerancePercent &&
+        percent <= (kMaxPercent - kOutlierTolerancePercent)) {
+        return false;
+    }
+
+    const auto iter = std::min_element(mTimestamps.begin(), mTimestamps.end(),
+                                       [timestamp](nsecs_t a, nsecs_t b) {
+                                           return std::abs(timestamp - a) < std::abs(timestamp - b);
+                                       });
+    const auto distancePercent = std::abs(*iter - timestamp) * kMaxPercent / mIdealPeriod;
+    if (distancePercent < kOutlierTolerancePercent) {
+        // duplicate timestamp
+        return false;
+    }
+    return true;
 }
 
 nsecs_t VSyncPredictor::currentPeriod() const {