(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/sigslot_repeater.h b/rtc_base/sigslot_repeater.h
index 724e624..f562c5a 100644
--- a/rtc_base/sigslot_repeater.h
+++ b/rtc_base/sigslot_repeater.h
@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef RTC_BASE_SIGSLOTREPEATER_H__
-#define RTC_BASE_SIGSLOTREPEATER_H__
+#ifndef RTC_BASE_SIGSLOT_REPEATER_H__
+#define RTC_BASE_SIGSLOT_REPEATER_H__
 
 // repeaters are both signals and slots, which are designed as intermediate
 // pass-throughs for signals and slots which don't know about each other (for
@@ -53,4 +53,4 @@
 
 }  // namespace sigslot
 
-#endif  // RTC_BASE_SIGSLOTREPEATER_H__
+#endif  // RTC_BASE_SIGSLOT_REPEATER_H__