Add command line argument to specify the rendertests file.

Change-Id: I53a8c2f168108fa5003c54ffece67fc20c38bb09
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/275137
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: John Rosasco <rosasco@google.com>
Commit-Queue: John Rosasco <rosasco@google.com>
6 files changed