Update libwebp to 0.4.0

third_party/libwebp/dec/quant.c

Index: third_party/libwebp/dec/quant.c
diff --git a/third_party/libwebp/dec/quant.c b/third_party/libwebp/dec/quant.c
index a4cc693db760c602c786636565516c8c7b869770..5b648f942c5e7d4ad2aaa7dff16ab9d4e32e94f0 100644
--- a/third_party/libwebp/dec/quant.c
+++ b/third_party/libwebp/dec/quant.c
@@ -13,10 +13,6 @@
 
 #include "./vp8i.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 static WEBP_INLINE int clip(int v, int M) {
   return v < 0 ? 0 : v > M ? M : v;
 }
@@ -104,12 +100,11 @@ void VP8ParseQuant(VP8Decoder* const dec) {
 
       m->uv_mat_[0] = kDcTable[clip(q + dquv_dc, 117)];
       m->uv_mat_[1] = kAcTable[clip(q + dquv_ac, 127)];
+
+      m->uv_quant_ = q + dquv_ac;   // for dithering strength evaluation
     }
   }
 }
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif