[packman] Chromium / chromium-ffmpeg H264 support

[Mark Fairbairn]

I don't know if the problem lies within chromium-ffmpeg or chromium 
itself but in the combination of Chromium (54.0.2840.90-85.1) & 
chromium-ffmpeg (54.0.2840.90-86.1) there is no H264 playback support. 
Youtube reports that h264 not supported in the browser and other sites 
refuse playback or fallback to another format.
Rolling Chromium back to 53.xx (but keeping chromium-ffmpeg 54.xx in 
place) resolves the issue.
Anybody know where the problem lies?