[readability-container-size-empty] Use empty() to check for emptiness.

Bug: None
Change-Id: If3cefd0f50521357a7fadef661954d2845246db6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/146718
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28683}

rtc_tools/rtc_event_log_visualizer/plot_base.cc

@@ -88,7 +88,7 @@ void Plot::AppendIntervalSeries(IntervalSeries&& interval_series) {
 }
 
 void Plot::AppendTimeSeriesIfNotEmpty(TimeSeries&& time_series) {
-  if (time_series.points.size() > 0) {
+  if (!time_series.points.empty()) {
     series_list_.emplace_back(std::move(time_series));
   }
 }