Update libwebp to 0.4.0

third_party/libwebp/dec/layer.c

 // Copyright 2011 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.
 // -----------------------------------------------------------------------------
 //
 // Enhancement layer (for YUV444/422)
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
 #include <assert.h>
 #include <stdlib.h>
 
 #include "./vp8i.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 //------------------------------------------------------------------------------
 
 int VP8DecodeLayer(VP8Decoder* const dec) {
   assert(dec);
   assert(dec->layer_data_size_ > 0);
   (void)dec;
 
   // TODO: handle enhancement layer here.
 
   return 1;
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif