libwebp: update to v0.5.1

third_party/libwebp/utils/quant_levels_dec.h

Index: third_party/libwebp/utils/quant_levels_dec.h
diff --git a/third_party/libwebp/utils/quant_levels_dec.h b/third_party/libwebp/utils/quant_levels_dec.h
index 9aab06807626315359a4b47dcf927f4dcba77877..59a13495d335a432ab9151d474eba14a273b59ab 100644
--- a/third_party/libwebp/utils/quant_levels_dec.h
+++ b/third_party/libwebp/utils/quant_levels_dec.h
@@ -21,11 +21,11 @@ extern "C" {
 #endif
 
 // Apply post-processing to input 'data' of size 'width'x'height' assuming that
-// the source was quantized to a reduced number of levels.
+// the source was quantized to a reduced number of levels. 'stride' is in bytes.
 // Strength is in [0..100] and controls the amount of dithering applied.
 // Returns false in case of error (data is NULL, invalid parameters,
 // malloc failure, ...).
-int WebPDequantizeLevels(uint8_t* const data, int width, int height,
+int WebPDequantizeLevels(uint8_t* const data, int width, int height, int stride,
                          int strength);
 
 #ifdef __cplusplus