Ignore negative cadence values.

media/filters/video_cadence_estimator.cc

Index: media/filters/video_cadence_estimator.cc
diff --git a/media/filters/video_cadence_estimator.cc b/media/filters/video_cadence_estimator.cc
index 7548b8277051a0d9e9b659aeb1ca75947d1d2ce7..ee8916e0c048001056d5089f0971e83e1b6b0b2a 100644
--- a/media/filters/video_cadence_estimator.cc
+++ b/media/filters/video_cadence_estimator.cc
@@ -189,6 +189,8 @@ VideoCadenceEstimator::Cadence VideoCadenceEstimator::CalculateCadence(
   // within minimum_time_until_max_drift.
   if (max_acceptable_drift >= minimum_time_until_max_drift_) {
     int cadence_value = round(perfect_cadence);
+    if (cadence_value < 0)
+      return Cadence();
     if (cadence_value == 0)
       cadence_value = 1;
     Cadence result = ConstructCadence(cadence_value, 1);