skhdr::AdaptiveGlobalToneMap: Add missing SK_API Bug: 468928417 Change-Id: I4735da65127bbcc14bd7cab9deb292f8bf68f141 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1137917 Commit-Queue: Christopher Cameron <ccameron@google.com> Reviewed-by: Kaylee Lubick <kjlubick@google.com> Reviewed-by: Christopher Cameron <ccameron@google.com>