Force Index8 to N32 in deferred texture path.

Ganesh doesn't support Index8, because GPUs don't really
support it. So serializing it in the deferred blob just
meant doing an expansion before upload. This forces that
to happen when we build the blob. It also paves the way
for removing the last usage of MakeTextureFromPixmap,
which I'd like to remove.

BUG=skia:

Change-Id: I7c0292098d71e2f8ec1f9910e1234761822ce957
Reviewed-on: https://skia-review.googlesource.com/7340
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed