Fix colorType/alphaType checks in SkCodec

src/codec/SkCodecPriv.h

 /*
  * Copyright 2015 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCodecPriv_DEFINED
 #define SkCodecPriv_DEFINED
 
@@ skipping 118 matching lines @@
     // Ensure the alpha type is valid
     if (!valid_alpha(dst.alphaType(), src.alphaType())) {
         return false;
     }
 
     // Check for supported color types
     switch (dst.colorType()) {
         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();
     }
 }
 
 /*
  * If there is a color table, get a pointer to the colors, otherwise return nullptr
  */
 inline const SkPMColor* get_color_ptr(SkColorTable* colorTable) {
@@ skipping 92 matching lines @@
     uint32_t result;
     memcpy(&result, &(buffer[i]), 4);
 #ifdef SK_CPU_BENDIAN
     return SkEndianSwap32(result);
 #else
     return result;
 #endif
 }
 
 #endif // SkCodecPriv_DEFINED