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

third_party/libwebp/webp/types.h

 // Copyright 2010 Google Inc.
 //
 // This code is licensed under the same terms as WebM:
 //  Software License Agreement:  http://www.webmproject.org/license/software/
 //  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
 // -----------------------------------------------------------------------------
 //
 //  Common types
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
 #ifndef WEBP_WEBP_TYPES_H_
 #define WEBP_WEBP_TYPES_H_
 
+#include <stddef.h>  // for size_t
+
 #ifndef _MSC_VER
 #include <inttypes.h>
 #else
 typedef signed   char int8_t;
 typedef unsigned char uint8_t;
 typedef signed   short int16_t;
 typedef unsigned short uint16_t;
 typedef signed   int int32_t;
 typedef unsigned int uint32_t;
 typedef unsigned long long int uint64_t;
 typedef long long int int64_t;
 #define inline __forceinline
 #endif  /* _MSC_VER */
 
 #ifndef WEBP_EXTERN
 // This explicitly marks library functions and allows for changing the
 // signature for e.g., Windows DLL builds.
 #define WEBP_EXTERN(type) extern type
 #endif  /* WEBP_EXTERN */
 
 #endif  /* WEBP_WEBP_TYPES_H_ */