(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.h b/test/testsupport/file_utils.h
index 8a18698..cdf3a31 100644
--- a/test/testsupport/file_utils.h
+++ b/test/testsupport/file_utils.h
@@ -10,8 +10,8 @@
 
 #include <stdio.h>
 
-#ifndef TEST_TESTSUPPORT_FILEUTILS_H_
-#define TEST_TESTSUPPORT_FILEUTILS_H_
+#ifndef TEST_TESTSUPPORT_FILE_UTILS_H_
+#define TEST_TESTSUPPORT_FILE_UTILS_H_
 
 #include <string>
 #include <vector>
@@ -106,4 +106,4 @@
 }  // namespace test
 }  // namespace webrtc
 
-#endif  // TEST_TESTSUPPORT_FILEUTILS_H_
+#endif  // TEST_TESTSUPPORT_FILE_UTILS_H_