(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/atomic_ops.h b/rtc_base/atomic_ops.h
index 16fa603..18a24a8 100644
--- a/rtc_base/atomic_ops.h
+++ b/rtc_base/atomic_ops.h
@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef RTC_BASE_ATOMICOPS_H_
-#define RTC_BASE_ATOMICOPS_H_
+#ifndef RTC_BASE_ATOMIC_OPS_H_
+#define RTC_BASE_ATOMIC_OPS_H_
 
 #if defined(WEBRTC_WIN)
 // clang-format off
@@ -76,4 +76,4 @@
 
 }  // namespace rtc
 
-#endif  // RTC_BASE_ATOMICOPS_H_
+#endif  // RTC_BASE_ATOMIC_OPS_H_