[bazel] //gm/gm.h: Add method getGoldKeys().

This method will return Gold keys that are specific to the GM. Only those GMs with GM-specific keys, such as codec GMs, need to override this method.

Bug: b/40045301
Change-Id: Ib72abe5cdfeab35a2f3b26203d4eb25a691ec3b0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/741676
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed