(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/api/data_channel_interface.h b/api/data_channel_interface.h
index 7cb5582..91a9804 100644
--- a/api/data_channel_interface.h
+++ b/api/data_channel_interface.h
@@ -11,16 +11,16 @@
 // This file contains interfaces for DataChannels
 // http://dev.w3.org/2011/webrtc/editor/webrtc.html#rtcdatachannel
 
-#ifndef API_DATACHANNELINTERFACE_H_
-#define API_DATACHANNELINTERFACE_H_
+#ifndef API_DATA_CHANNEL_INTERFACE_H_
+#define API_DATA_CHANNEL_INTERFACE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 #include <string>
 
 #include "rtc_base/checks.h"
-#include "rtc_base/copyonwritebuffer.h"
-#include "rtc_base/refcount.h"
+#include "rtc_base/copy_on_write_buffer.h"
+#include "rtc_base/ref_count.h"
 
 namespace webrtc {
 
@@ -177,4 +177,4 @@
 
 }  // namespace webrtc
 
-#endif  // API_DATACHANNELINTERFACE_H_
+#endif  // API_DATA_CHANNEL_INTERFACE_H_