Configuring chromium build options

[ramysiha]

Generally when building chromium, I can use ng args to generate the args.gn files that would contain different chromium build options like:

Build arguments go here.

See "gn args <out_dir> --list" for available build arguments.

media_use_ffmpeg=false
media_use_libvpx=false
media_use_libwebm=false

Problem is that usually that file is generated at out/Default directory, and I'm not sure what will be the equivalent path for that when building chromium through the QtWebengine. I've also read that setting the GYP_DEFINES env variable should do the trick, but I haven't tried it yet.