This refactors the current gn_to_bp script and moves the common
components into a utils class. Both gn_to_bp scripts now also
accept an optional param (--gn <gn_path>) to make it easier to run
within the Android tree where we don't have the DEPS synced.
Change-Id: Idc4de7b3993e63e21a5b7137b1873d82a8e1843e
Reviewed-on: https://skia-review.googlesource.com/102184
Commit-Queue: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
