Improvements to uses of base::SmallMap

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 36e3a62aa055b57b6ba52d9ef6576e4d6824d3ba..5af7b4cd14a8d2a969e141603f612094d652c2ba 100644
--- a/cc/scheduler/begin_frame_source.cc
+++ b/cc/scheduler/begin_frame_source.cc
@@ -345,8 +345,6 @@ uint64_t BeginFrameObserverAckTracker::LatestConfirmedSequenceNumber() const {
 
 void BeginFrameObserverAckTracker::AsValueInto(
     base::trace_event::TracedValue* state) const {
-  base::SmallMap<std::map<BeginFrameObserver*, uint64_t>, 4>
-      latest_confirmed_sequence_numbers_;
   state->SetInteger("current_source_id", current_source_id_);
   state->SetInteger("current_sequence_number", current_sequence_number_);
   state->SetInteger("num_observers", observers_.size());