Disable dithering in libjpeg-turbo for 565 decodes

src/codec/SkJpegCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkJpegCodec.h"
 #include "SkJpegDecoderMgr.h"
@@ skipping 228 matching lines @@
                 // current platform
 #if defined(SK_PMCOLOR_IS_RGBA)
                 fDecoderMgr->dinfo()->out_color_space = JCS_EXT_RGBA;
 #else
                 fDecoderMgr->dinfo()->out_color_space = JCS_EXT_BGRA;
 #endif
             }
             return true;
         case kRGB_565_SkColorType:
             if (isCMYK) {
+                // FIXME (msarett): We need to support 565 here.  It's not hard to do, considering
+                // we already convert CMYK to RGBA, I just need to do it.  I think it might be
+                // best to do this in SkSwizzler and also move convert_CMYK_to_RGBA into SkSwizzler.
                 return false;
             } else {
+                fDecoderMgr->dinfo()->dither_mode = JDITHER_NONE;
                 fDecoderMgr->dinfo()->out_color_space = JCS_RGB565;
             }
             return true;
         case kGray_8_SkColorType:
             if (isCMYK) {
                 return false;
             } else {
                 // We will enable decodes to gray even if the image is color because this is
                 // much faster than decoding to color and then converting
                 fDecoderMgr->dinfo()->out_color_space = JCS_GRAYSCALE;
@@ skipping 312 matching lines @@
     SkAutoTDelete<SkJpegCodec> codec(static_cast<SkJpegCodec*>(SkJpegCodec::NewFromStream(stream)));
     if (!codec) {
         return nullptr;
     }
 
     const SkImageInfo& srcInfo = codec->getInfo();
 
     // Return the new scanline decoder
     return new SkJpegScanlineDecoder(srcInfo, codec.detach());
 }