[Pkg-chromium-maint] Bug#632903: Chromium armel fixes

[Riku Voipio]

tags 632903 +patch
thanks

Hi,

The following patch fixes building chromium on debian/armel and prepares
the way for debian/armhf builds.

1) add libegl1-mesa-dev and libgles2-mesa-dev to arm build depends, as the
webgl code on arm uses GLES instead of GL.

2) Really use system vpx so that the initial gyp dependency error on arm goes away.
Adding -lvpx to ffmpeg.gyp is not exactly the correct place. but there is no use_system_vpx
define anywhere, which would seem a more correct place...

3) force cups on and disable webrtc for now. 

4) fix building SKIA on < armv7

5) as bonus point, add patch to build with current libav.

Riku