Ensure that we allocate 32-bit pixels in GM's generator

It's possible that we want to ask the generator to generate in a
different colorType, which would break the assumptions later in this
function.

Bug: skia:
Change-Id: I4495e01a8829d017887150aa78998f407df354e4
Reviewed-on: https://skia-review.googlesource.com/c/163886
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed