(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/signal_thread.h b/rtc_base/signal_thread.h
index 9208e2c..9a20ad2 100644
--- a/rtc_base/signal_thread.h
+++ b/rtc_base/signal_thread.h
@@ -8,16 +8,16 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef RTC_BASE_SIGNALTHREAD_H_
-#define RTC_BASE_SIGNALTHREAD_H_
+#ifndef RTC_BASE_SIGNAL_THREAD_H_
+#define RTC_BASE_SIGNAL_THREAD_H_
 
 #include <string>
 
 #include "rtc_base/checks.h"
-#include "rtc_base/constructormagic.h"
-#include "rtc_base/criticalsection.h"
-#include "rtc_base/messagehandler.h"
-#include "rtc_base/messagequeue.h"
+#include "rtc_base/constructor_magic.h"
+#include "rtc_base/critical_section.h"
+#include "rtc_base/message_handler.h"
+#include "rtc_base/message_queue.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"
 #include "rtc_base/thread.h"
 #include "rtc_base/thread_annotations.h"
@@ -155,4 +155,4 @@
 
 }  // namespace rtc
 
-#endif  // RTC_BASE_SIGNALTHREAD_H_
+#endif  // RTC_BASE_SIGNAL_THREAD_H_