(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/pc/data_channel.h b/pc/data_channel.h
index 55a52db..af8dd93 100644
--- a/pc/data_channel.h
+++ b/pc/data_channel.h
@@ -8,19 +8,19 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef PC_DATACHANNEL_H_
-#define PC_DATACHANNEL_H_
+#ifndef PC_DATA_CHANNEL_H_
+#define PC_DATA_CHANNEL_H_
 
 #include <deque>
 #include <memory>
 #include <set>
 #include <string>
 
-#include "api/datachannelinterface.h"
+#include "api/data_channel_interface.h"
 #include "api/proxy.h"
-#include "media/base/mediachannel.h"
+#include "media/base/media_channel.h"
 #include "pc/channel.h"
-#include "rtc_base/asyncinvoker.h"
+#include "rtc_base/async_invoker.h"
 #include "rtc_base/scoped_ref_ptr.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"
 
@@ -313,4 +313,4 @@
 
 }  // namespace webrtc
 
-#endif  // PC_DATACHANNEL_H_
+#endif  // PC_DATA_CHANNEL_H_