limit transfer buffer workaround to angle d3d backend

Tested that this works ok on GL backend of ANGLE.

Change-Id: I517523e03d49b3bc85abdda31ee427d708db0c7b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/407817
Auto-Submit: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
1 file changed