libwebp: update to 0.4.2-rc2

third_party/libwebp/dec/frame.c

 // Copyright 2010 Google Inc. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the COPYING file in the root of the source
 // tree. An additional intellectual property rights grant can be found
 // in the file PATENTS. All contributing project authors may
 // be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Frame-reconstruction function. Memory allocation.
@@ skipping 159 matching lines @@
           const int idx = (dqm->uv_quant_ < 0) ? 0 : dqm->uv_quant_;
           dqm->dither_ = (f * kQuantToDitherAmp[idx]) >> 3;
         }
         all_amp |= dqm->dither_;
       }
       if (all_amp != 0) {
         VP8InitRandom(&dec->dithering_rg_, 1.0f);
         dec->dither_ = 1;
       }
     }
-#if WEBP_DECODER_ABI_VERSION > 0x0203
+#if WEBP_DECODER_ABI_VERSION > 0x0204
     // potentially allow alpha dithering
     dec->alpha_dithering_ = options->alpha_dithering_strength;
     if (dec->alpha_dithering_ > 100) {
       dec->alpha_dithering_ = 100;
     } else if (dec->alpha_dithering_ < 0) {
       dec->alpha_dithering_ = 0;
     }
 #endif
   }
 }
@@ skipping 628 matching lines @@
       for (j = 0; j < 8; ++j) {
         memcpy(u_out + j * dec->cache_uv_stride_, u_dst + j * BPS, 8);
         memcpy(v_out + j * dec->cache_uv_stride_, v_dst + j * BPS, 8);
       }
     }
   }
 }
 
 //------------------------------------------------------------------------------