example_util: add ExUtilSetBinaryMode

use it in dwebp when dealing with 'stdout'

Change-Id: I8b8a0b0de9e73731e913ac3c83b5e2b33c693175
diff --git a/examples/example_util.h b/examples/example_util.h
index bf90c35..4ef703d 100644
--- a/examples/example_util.h
+++ b/examples/example_util.h
@@ -13,12 +13,17 @@
 #ifndef WEBP_EXAMPLES_EXAMPLE_UTIL_H_
 #define WEBP_EXAMPLES_EXAMPLE_UTIL_H_
 
+#include <stdio.h>
 #include "webp/decode.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+// Reopen file in binary (O_BINARY) mode.
+// Returns 'file' on success, NULL otherwise.
+FILE* ExUtilSetBinaryMode(FILE* file);
+
 // Allocates storage for entire file 'file_name' and returns contents and size
 // in 'data' and 'data_size'. Returns 1 on success, 0 otherwise. '*data' should
 // be deleted using free().