lookup received factories directly

Instead of mapping int -> name -> factory, map int -> factory.

The counterpart of https://skia-review.googlesource.com/c/skia/+/168264,
this time for the receiver.

Change-Id: I8c7756b1e5519611e72cba7d4aa88976169375af
Reviewed-on: https://skia-review.googlesource.com/c/171044
Reviewed-by: Khushal Sagar <khushalsagar@chromium.org>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed