(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/peer_connection_factory_proxy.h b/api/peer_connection_factory_proxy.h
index d885cc1..1f37034 100644
--- a/api/peer_connection_factory_proxy.h
+++ b/api/peer_connection_factory_proxy.h
@@ -8,14 +8,14 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef API_PEERCONNECTIONFACTORYPROXY_H_
-#define API_PEERCONNECTIONFACTORYPROXY_H_
+#ifndef API_PEER_CONNECTION_FACTORY_PROXY_H_
+#define API_PEER_CONNECTION_FACTORY_PROXY_H_
 
 #include <memory>
 #include <string>
 #include <utility>
 
-#include "api/peerconnectioninterface.h"
+#include "api/peer_connection_interface.h"
 #include "api/proxy.h"
 #include "rtc_base/bind.h"
 
@@ -74,4 +74,4 @@
 
 }  // namespace webrtc
 
-#endif  // API_PEERCONNECTIONFACTORYPROXY_H_
+#endif  // API_PEER_CONNECTION_FACTORY_PROXY_H_