***Disables swizzles to 565.

***Disables swizzles to 565.
We may want to enable swizzles to 565
for images that are encoded in a format
similar to 565, however, we do not want
to take images that decode naturally to
kN32 and then convert them to 565.

***Enable swizzles to kIndex_8.  For images
encoded in a color table format, we suggest
that they be decoded to kIndex_8.  When we
decode, we only allow conversion to kIndex_8
if it matches the suggested color type (except
wbmp which seems good as is).

***Modify dm to test images that decode to
kIndex_8.

BUG=skia:3257
BUG=skia:3440

Review URL: https://codereview.chromium.org/1055743003