Add SkMakeUnique to gn

Change-Id: Ic1bee4551d471c4451837a93c14d49edc7c0f760
Reviewed-on: https://skia-review.googlesource.com/129314
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed