Fix some missed stdlib includes

Ran into these when trying a newer libstdc++

Bug: None
Change-Id: Ie3ce0ae1ae1e6da1a15476fbf942b48b37adc9fa
Reviewed-on: https://webrtc-review.googlesource.com/23501
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20701}
diff --git a/rtc_tools/event_log_visualizer/analyzer.cc b/rtc_tools/event_log_visualizer/analyzer.cc
index c351b78..0ef0803 100644
--- a/rtc_tools/event_log_visualizer/analyzer.cc
+++ b/rtc_tools/event_log_visualizer/analyzer.cc
@@ -11,6 +11,7 @@
 #include "rtc_tools/event_log_visualizer/analyzer.h"
 
 #include <algorithm>
+#include <cmath>
 #include <limits>
 #include <map>
 #include <sstream>