The bundled ffmpeg in Chromium is newer than the one in Guix.  Patch so
we can build with the new and old ffmpeg versions.

Taken from Gentoo:
https://gitweb.gentoo.org/repo/gentoo.git/tree/www-client/chromium/files/chromium-93-fix-build-with-system-ffmpeg.patch

diff --git a/media/filters/audio_decoder_unittest.cc b/media/filters/audio_decoder_unittest.cc
--- a/media/filters/audio_decoder_unittest.cc
+++ b/media/filters/audio_decoder_unittest.cc
@@ -109,7 +109,11 @@ void SetDiscardPadding(AVPacket* packet,
   }
 
   // If the timestamp is positive, try to use FFmpeg's discard data.
+#if LIBAVUTIL_VERSION_MAJOR < 57
+  int skip_samples_size = 0;
+#else
   size_t skip_samples_size = 0;
+#endif
   const uint32_t* skip_samples_ptr =
       reinterpret_cast<const uint32_t*>(av_packet_get_side_data(
           packet, AV_PKT_DATA_SKIP_SAMPLES, &skip_samples_size));
diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
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