libgifcodec is based on a fork of libgif made by Chromium. It was copied into Skia with https://codereview.chromium.org/2045293002, as https://skia.googlesource.com/skia/+/19b91531e912283d237435d94516575b28713cba.
The header file SkGifCodec.h exposes two functions:
bool SkGifCodec::IsGif(const void*, size_t);
std::unique_ptr<SkCodec> SkGifCodec::MakeFromStream(std::unique_ptr<SkStream>, SkCodec::Result*);
Which can be used by Skia's SkCodec::MakeFromStream to implement GIF Decoding.
See LICENSE.md for the license information.