add flag to fix google3

Bug: skia:
Change-Id: Icbaf4737d4f8d45c969811cebc53da20b0f5d954
Reviewed-on: https://skia-review.googlesource.com/88422
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/public.bzl b/public.bzl
index 1e28940..412324c 100644
--- a/public.bzl
+++ b/public.bzl
@@ -586,6 +586,7 @@
       "SK_JUMPER_DISABLE_8BIT",
       # JPEG is in codec_limited
       "SK_HAS_JPEG_LIBRARY",
+      "SK_SUPPORT_LEGACY_SERIALPROCS_REF",
   ] + skia_select(
       os_conditions,
       [