Safely handle unsupported color xforms in SkCodec

(1) The transformation code *should* support any src SkColorSpace
that we successfully parse.  This is agreed upon internally and
by clients.  The fact that we currently don't is just a bug...
(2) We cannot and will not support all SkColorSpaces as dsts.

So if we fail to make a SkColorSpaceXform, we should assume that
it was caused by a bad dst color space.  The correct response in
this case is to return kInvalidConversion.  I've rewritten the CL
to do this.

The fact that weird src spaces will sometimes trigger a
kInvalidConversion is just a bug that is being actively worked on.

TBR=reed@google.com

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3661

Change-Id: Iac2b45120507ec71b1b3d555c61931f7348dad9e
Reviewed-on: https://skia-review.googlesource.com/3661
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Robert Aftias <raftias@google.com>
8 files changed