libwebp: update to v0.5.1

third_party/libwebp/enc/picture_psnr.c

Index: third_party/libwebp/enc/picture_psnr.c
diff --git a/third_party/libwebp/enc/picture_psnr.c b/third_party/libwebp/enc/picture_psnr.c
index 40214efc95253b995b1f95e77e674f55a7dcf14f..81ab1b5ca1c371c677035fe75d5b7c5661985ed2 100644
--- a/third_party/libwebp/enc/picture_psnr.c
+++ b/third_party/libwebp/enc/picture_psnr.c
@@ -27,7 +27,7 @@
 
 static void AccumulateLSIM(const uint8_t* src, int src_stride,
                            const uint8_t* ref, int ref_stride,
-                           int w, int h, DistoStats* stats) {
+                           int w, int h, VP8DistoStats* stats) {
   int x, y;
   double total_sse = 0.;
   for (y = 0; y < h; ++y) {
@@ -71,11 +71,13 @@ static float GetPSNR(const double v) {
 
 int WebPPictureDistortion(const WebPPicture* src, const WebPPicture* ref,
                           int type, float result[5]) {
-  DistoStats stats[5];
+  VP8DistoStats stats[5];
   int w, h;
 
   memset(stats, 0, sizeof(stats));
 
+  VP8SSIMDspInit();
+
   if (src == NULL || ref == NULL ||
       src->width != ref->width || src->height != ref->height ||
       src->use_argb != ref->use_argb || result == NULL) {