Finish supporting decoding opaque to non-opaque

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 114 matching lines @@
     if (!valid_alpha(dst.alphaType(), src.alphaType())) {
         return false;
     }
 
     // Check for supported color types
     switch (dst.colorType()) {
         case kRGBA_8888_SkColorType:
         case kBGRA_8888_SkColorType:
             return true;
         case kRGB_565_SkColorType:
-            return kOpaque_SkAlphaType == dst.alphaType();
-        case kGray_8_SkColorType:
-            if (kOpaque_SkAlphaType != dst.alphaType()) {
-                return false;
-            }
-            // Fall through
+            return kOpaque_SkAlphaType == src.alphaType();
         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) {
      return nullptr != colorTable ? colorTable->readColors() : nullptr;
@@ skipping 164 matching lines @@
     } else {
         if (isRGBA) {
             return &SkPackARGB_as_RGBA;
         } else {
             return &SkPackARGB_as_BGRA;
         }
     }
 }
 
 #endif // SkCodecPriv_DEFINED