Add legacy flag for vulkan interface for flutter.

Bug: skia:
Change-Id: I50eb5c331b4a5818037155865d477914276a983c
Reviewed-on: https://skia-review.googlesource.com/137194
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
1 file changed