Avoid DCHECK in ExternalBeginFrameSource::GetMissedBeginFrameArgs caused by out of order frame time

cc/scheduler/begin_frame_source.cc

Index: cc/scheduler/begin_frame_source.cc
diff --git a/cc/scheduler/begin_frame_source.cc b/cc/scheduler/begin_frame_source.cc
index 5b4cd4048fcdfbed5889ee66de3f8815b2053e88..c5ec59595c2015ee90777c806a436440cf0b8a79 100644
--- a/cc/scheduler/begin_frame_source.cc
+++ b/cc/scheduler/begin_frame_source.cc
@@ -337,7 +337,7 @@ BeginFrameArgs ExternalBeginFrameSource::GetMissedBeginFrameArgs(
 
   const BeginFrameArgs& last_args = obs->LastUsedBeginFrameArgs();
   if (last_args.IsValid() &&
-      last_begin_frame_args_.frame_time == last_args.frame_time) {
+      last_begin_frame_args_.frame_time <= last_args.frame_time) {
     return BeginFrameArgs();
   }