Event log visualizer TimeSeries is now created on the stack and then moved into the vector of series.

BUG=none

Review-Url: https://codereview.webrtc.org/2824973003
Cr-Commit-Position: refs/heads/master@{#17763}
diff --git a/webrtc/tools/event_log_visualizer/plot_base.h b/webrtc/tools/event_log_visualizer/plot_base.h
index b2ab299..afa20be 100644
--- a/webrtc/tools/event_log_visualizer/plot_base.h
+++ b/webrtc/tools/event_log_visualizer/plot_base.h
@@ -34,10 +34,9 @@
 
 struct TimeSeries {
   TimeSeries() = default;
-  TimeSeries(const char* label, PlotStyle style)
-      : label(label), style(style), points() {}
+  TimeSeries(const char* label, PlotStyle style) : label(label), style(style) {}
   TimeSeries(const std::string& label, PlotStyle style)
-      : label(label), style(style), points() {}
+      : label(label), style(style) {}
   TimeSeries(TimeSeries&& other)
       : label(std::move(other.label)),
         style(other.style),
@@ -108,10 +107,7 @@
   void SetTitle(std::string title);
 
   // Add a new TimeSeries to the plot.
-  TimeSeries* AddTimeSeries(const char* label, PlotStyle style);
-  TimeSeries* AddTimeSeries(const std::string& label, PlotStyle style);
-
-  std::vector<TimeSeries> series_list_;
+  void AppendTimeSeries(TimeSeries&& time_series);
 
  protected:
   float xaxis_min_;
@@ -121,6 +117,7 @@
   float yaxis_max_;
   std::string yaxis_label_;
   std::string title_;
+  std::vector<TimeSeries> series_list_;
 };
 
 class PlotCollection {