Change bitmap initialization in DrawFunctions fuzzer

BUG=skia:

Change-Id: Ibfd778315a0c3bf6c3abc23f8935c485fab89366
Reviewed-on: https://skia-review.googlesource.com/8615
Reviewed-by: twsmith@mozilla.com <twsmith@mozilla.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
1 file changed