(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/testsupport/file_utils.cc b/test/testsupport/file_utils.cc
index 45f7091..45b2bc2 100644
--- a/test/testsupport/file_utils.cc
+++ b/test/testsupport/file_utils.cc
@@ -8,7 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "test/testsupport/fileutils.h"
+#include "test/testsupport/file_utils.h"
 
 #include <assert.h>
 
@@ -47,16 +47,16 @@
 #include <utility>
 
 #if defined(WEBRTC_IOS)
-#include "test/testsupport/iosfileutils.h"
+#include "test/testsupport/ios_file_utils.h"
 #endif
 
 #if defined(WEBRTC_MAC)
-#include "test/testsupport/macfileutils.h"
+#include "test/testsupport/mac_file_utils.h"
 #endif
 
 #include "rtc_base/checks.h"
-#include "rtc_base/stringutils.h"
-#include "test/testsupport/fileutils_override.h"
+#include "rtc_base/string_utils.h"
+#include "test/testsupport/file_utils_override.h"
 
 namespace webrtc {
 namespace test {