Fix NoGPU compilation

All of these functions were written to work without GPU support, just
forgot to compile them in that situation.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4796

Change-Id: Ia23d304f07eb16714390b459dd448bc08402f479
Reviewed-on: https://skia-review.googlesource.com/4796
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Stan Iliev <stani@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Stan Iliev <stani@google.com>