Angle's existing GN files only work in Chrome, so I've written a new one.
This won't work on Windows, but our GN build doesn't work on Windows anyway. So this CL is an attempt to get a ahead of that curve on ANGLE. It looks large but fairly straightforward.
Now working on Linux:
$ gn gen angle --args=skia_use_angle=true
$ ninja -C angle
$ angle/dm --config angle-gl --src gm -w dm-out
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2361983002
Review-Url: https://codereview.chromium.org/2361983002
