Replace NULL with nullptr in all C++ files.

webrtc/modules/remote_bitrate_estimator/inter_arrival.cc

Index: webrtc/modules/remote_bitrate_estimator/inter_arrival.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/inter_arrival.cc b/webrtc/modules/remote_bitrate_estimator/inter_arrival.cc
index 1b2dc43db227a6567f300d0b634285e199b16738..d1b9796ddbc546eddeb6e061db43fa239169c31b 100644
--- a/webrtc/modules/remote_bitrate_estimator/inter_arrival.cc
+++ b/webrtc/modules/remote_bitrate_estimator/inter_arrival.cc
@@ -37,9 +37,9 @@ bool InterArrival::ComputeDeltas(uint32_t timestamp,
                                  uint32_t* timestamp_delta,
                                  int64_t* arrival_time_delta_ms,
                                  int* packet_size_delta) {
-  assert(timestamp_delta != NULL);
-  assert(arrival_time_delta_ms != NULL);
-  assert(packet_size_delta != NULL);
+  assert(timestamp_delta != nullptr);
+  assert(arrival_time_delta_ms != nullptr);
+  assert(packet_size_delta != nullptr);
   bool calculated_deltas = false;
   if (current_timestamp_group_.IsFirstPacket()) {
     // We don't have enough data to update the filter, so we store it until we