(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/test/frame_generator.h b/test/frame_generator.h
index 45cc9f0..ba36d38 100644
--- a/test/frame_generator.h
+++ b/test/frame_generator.h
@@ -16,7 +16,7 @@
 
 #include "api/video/video_frame.h"
 #include "api/video/video_source_interface.h"
-#include "rtc_base/criticalsection.h"
+#include "rtc_base/critical_section.h"
 
 namespace webrtc {
 class Clock;