SkPDF: assert premultiplied bitmaps are valid in debug.

Change-Id: I5feeee9a02199c6f4aa91c67e19844e022175d23
Reviewed-on: https://skia-review.googlesource.com/17993
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed