gen_angle_gn_info_json.py can be used to generate a json description
of the build for given targets. This information can then be used
to generate build files for other tool chains (e.g. Android blueprint)

Bug: angleproject:2418
Change-Id: Ief8f43e30ae1f469e3fcfa795306675e29a90a2f
Reviewed-on: https://chromium-review.googlesource.com/967225
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>