(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/net_helpers.cc b/rtc_base/net_helpers.cc
index 1bba3b4..c662f1a 100644
--- a/rtc_base/net_helpers.cc
+++ b/rtc_base/net_helpers.cc
@@ -8,7 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "rtc_base/nethelpers.h"
+#include "rtc_base/net_helpers.h"
 
 #include <memory>
 
@@ -19,14 +19,14 @@
 #endif
 #if defined(WEBRTC_POSIX) && !defined(__native_client__)
 #if defined(WEBRTC_ANDROID)
-#include "rtc_base/ifaddrs-android.h"
+#include "rtc_base/ifaddrs_android.h"
 #else
 #include <ifaddrs.h>
 #endif
 #endif  // defined(WEBRTC_POSIX) && !defined(__native_client__)
 
 #include "rtc_base/logging.h"
-#include "rtc_base/signalthread.h"
+#include "rtc_base/signal_thread.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"  // for signal_with_thread...
 
 namespace rtc {