Improve color type handling in SkImage_Base::makeColorSpace()

Color space xforms  with Alpha8 images are no-ops.
Other xforms should use 8888 as dst color type.

BUG=skia:

Change-Id: Iede3d94d23c8f4c3dabdaa5450af7b5bfff8d24f
Reviewed-on: https://skia-review.googlesource.com/9996
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
2 files changed