Fix colorType/alphaType checks in SkCodec

src/codec/SkCodecPriv.h

Index: src/codec/SkCodecPriv.h
diff --git a/src/codec/SkCodecPriv.h b/src/codec/SkCodecPriv.h
index 235c4e24aff3bcbc56787487824170c33f6fd4fa..bcbd67b8f5fccba8e75a1926ad0aae0c0d5cd325 100644
--- a/src/codec/SkCodecPriv.h
+++ b/src/codec/SkCodecPriv.h
@@ -136,6 +136,7 @@ inline bool conversion_possible(const SkImageInfo& dst, const SkImageInfo& src)
         case kN32_SkColorType:
             return true;
         case kRGB_565_SkColorType:
+        case kGray_8_SkColorType:

[scroggo, 2016/02/12 17:13:55]

So if the Source is N32 and has no alpha, we will support converting to gray? Is
that true for all formats? For JPEG I understand that we can (although shouldn't
we be careful in case clients request ALPHA_8 meaning to get ALPHA_8 only if
it's gray?), but I think this is not true for all formats?

[msarett, 2016/02/12 17:41:31]

Oops this is not what I meant to do.  Just want to require that gray decodes are
opaque.

             return src.alphaType() == kOpaque_SkAlphaType;
         default:
             return dst.colorType() == src.colorType();