DEPS: add third_party/externals/libgifcodec

A later CL will remove:
    third_party/gif/*
    src/codec/SkGifCodec.*
and update the BUILD.gn file.

But first, a CL will make the Android roller pick up this DEP.

Bug: skia:9654
Change-Id: I12a63dd83f6b2fd11c299537686c5219581fcc13
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255083
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed