No one (other than test code) was using this API, and it lacks the context
to do the right thing. Specifically, if this forces a decode of an encoded
image, we don't know the intended use (re: color spaces) to determine how
we should decode.
BUG=skia:
Change-Id: I6ff700b3a5adce8257f35c5e3dd5ba557b2a3219
Reviewed-on: https://skia-review.googlesource.com/5614
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
