(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/media_stream_proxy.h b/api/media_stream_proxy.h
index 4c54459..5169679 100644
--- a/api/media_stream_proxy.h
+++ b/api/media_stream_proxy.h
@@ -8,12 +8,12 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef API_MEDIASTREAMPROXY_H_
-#define API_MEDIASTREAMPROXY_H_
+#ifndef API_MEDIA_STREAM_PROXY_H_
+#define API_MEDIA_STREAM_PROXY_H_
 
 #include <string>
 
-#include "api/mediastreaminterface.h"
+#include "api/media_stream_interface.h"
 #include "api/proxy.h"
 
 namespace webrtc {
@@ -41,4 +41,4 @@
 
 }  // namespace webrtc
 
-#endif  // API_MEDIASTREAMPROXY_H_
+#endif  // API_MEDIA_STREAM_PROXY_H_