Raise gyp/GN failure if proprietary_codecs=1 and ffmpeg_branding=Chromium

media/BUILD.gn

Index: media/BUILD.gn
diff --git a/media/BUILD.gn b/media/BUILD.gn
index afcadfdf74ec632b247a4b95ffc0ca83cea5cff6..317c1c1f0151a8d6c8790f0107fd0da7f231011a 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -11,6 +11,7 @@ import("//build/config/ui.gni")
 import("//media/media_options.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//testing/test.gni")
+import("//third_party/ffmpeg/ffmpeg_options.gni")
 
 buildflag_header("media_features") {
   header = "media_features.h"
@@ -22,6 +23,12 @@ buildflag_header("media_features") {
   ]
 }
 
+if (proprietary_codecs && media_use_ffmpeg) {
+  assert(
+      ffmpeg_branding != "Chromium",
+      "proprietary codecs and ffmpeg_branding set to Chromium are incompatible")
+}
+
 # Common configuration for targets in the media directory.
 # NOT for exporting.
 config("media_config") {