(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/api/proxy.h b/api/proxy.h
index 3c30995..b1d9d50 100644
--- a/api/proxy.h
+++ b/api/proxy.h
@@ -57,9 +57,9 @@
 #include <utility>
 
 #include "rtc_base/event.h"
-#include "rtc_base/messagehandler.h"
-#include "rtc_base/messagequeue.h"
-#include "rtc_base/refcountedobject.h"
+#include "rtc_base/message_handler.h"
+#include "rtc_base/message_queue.h"
+#include "rtc_base/ref_counted_object.h"
 #include "rtc_base/scoped_ref_ptr.h"
 #include "rtc_base/thread.h"