(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/examples/unityplugin/class_reference_holder.cc b/examples/unityplugin/class_reference_holder.cc
index 0ad96c5..00ca772 100644
--- a/examples/unityplugin/class_reference_holder.cc
+++ b/examples/unityplugin/class_reference_holder.cc
@@ -7,7 +7,7 @@
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
-#include "examples/unityplugin/classreferenceholder.h"
+#include "examples/unityplugin/class_reference_holder.h"
 
 #include <utility>