Add Skia xfermode test output to testing corpus.

BUG=pdfium:1152

Change-Id: Ia693a809a2d321c96cf93635547dfdac1f5e9342
Reviewed-on: https://pdfium-review.googlesource.com/42610
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
8 files changed