libwebp: fix some int <-> size_t mix for buffer sizes

third_party/libwebp/webp/decode.h

Index: third_party/libwebp/webp/decode.h
diff --git a/third_party/libwebp/webp/decode.h b/third_party/libwebp/webp/decode.h
index fe5fa4a11fd8d01d06f3b80a085110c919b28d89..507fe7f893981cec3a41e685fbbc3cef4f7cf16a 100644
--- a/third_party/libwebp/webp/decode.h
+++ b/third_party/libwebp/webp/decode.h
@@ -130,9 +130,9 @@ typedef struct {              // view as YUVA
   int y_stride;               // luma stride
   int u_stride, v_stride;     // chroma strides
   int a_stride;               // alpha stride
-  int y_size;                 // luma plane size
-  int u_size, v_size;         // chroma planes size
-  int a_size;                 // alpha-plane size
+  size_t y_size;              // luma plane size
+  size_t u_size, v_size;      // chroma planes size
+  size_t a_size;              // alpha-plane size
 } WebPYUVABuffer;
 
 // Output buffer