Reimplement Direct3D GetFunction(). Copied from old Shader::GetFunction(). Bug 22533227 Change-Id: I587a4112bc97f75c010b6f572f8f4388d5af9225 Reviewed-on: https://swiftshader-review.googlesource.com/3734 Reviewed-by: Nicolas Capens <capn@google.com> Tested-by: Nicolas Capens <capn@google.com>