Simplify the VideoFrameDumpingDecoder API.

This CL changes the VideoFrameDumpingDecoder API to only expose a
factory function creating the wrapper instead of the full class.

Bug: webrtc:10902
Change-Id: I1e7e3a60accea1a7c48207d4262ed4bacacab4a2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150040
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28924}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index e7f5a5b..634e40e 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -163,6 +163,7 @@
     "../modules/video_coding:video_codec_interface",
     "../modules/video_coding:video_coding_utility",
     "../rtc_base:rtc_base_approved",
+    "../rtc_base/system:file_wrapper",
     "//third_party/abseil-cpp/absl/memory",
   ]
 }