(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}

rtc_base/test_utils.h

@@ -8,15 +8,15 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef RTC_BASE_TESTUTILS_H_
-#define RTC_BASE_TESTUTILS_H_
+#ifndef RTC_BASE_TEST_UTILS_H_
+#define RTC_BASE_TEST_UTILS_H_
 
 // Utilities for testing rtc infrastructure in unittests
 
 #include <map>
 #include <utility>
 
-#include "rtc_base/asyncsocket.h"
+#include "rtc_base/async_socket.h"
 #include "rtc_base/stream.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"
 
@@ -137,4 +137,4 @@ class StreamSink : public sigslot::has_slots<> {
 }  // namespace testing
 }  // namespace webrtc
 
-#endif  // RTC_BASE_TESTUTILS_H_
+#endif  // RTC_BASE_TEST_UTILS_H_