(4) Rename files to snake_case: update BUILD.gn, include paths, header guards, and DEPS entries

Mechanically generated by running this command:

tools_webrtc/do-renames.sh update all-renames.txt && git cl format

Then manually updating:

tools_webrtc/sanitizers/tsan_suppressions_webrtc.cc

Bug: webrtc:10159
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I54824cd91dada8fc3ee3d098f971bc319d477833
Reviewed-on: https://webrtc-review.googlesource.com/c/115653
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26226}
diff --git a/rtc_base/one_time_event.h b/rtc_base/one_time_event.h
index f649f15..c5ccbf6 100644
--- a/rtc_base/one_time_event.h
+++ b/rtc_base/one_time_event.h
@@ -8,10 +8,10 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef RTC_BASE_ONETIMEEVENT_H_
-#define RTC_BASE_ONETIMEEVENT_H_
+#ifndef RTC_BASE_ONE_TIME_EVENT_H_
+#define RTC_BASE_ONE_TIME_EVENT_H_
 
-#include "rtc_base/criticalsection.h"
+#include "rtc_base/critical_section.h"
 
 namespace webrtc {
 // Provides a simple way to perform an operation (such as logging) one
@@ -57,4 +57,4 @@
 
 }  // namespace webrtc
 
-#endif  // RTC_BASE_ONETIMEEVENT_H_
+#endif  // RTC_BASE_ONE_TIME_EVENT_H_