Make a NaClDesc ctor for creating descs from NaClFileInfo.

src/trusted/desc/nacl_desc_file_info.h

+/*
+ * Copyright (c) 2014 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef NATIVE_CLIENT_SRC_TRUSTED_DESC_NACL_DESC_FILE_INFO_H_
+#define NATIVE_CLIENT_SRC_TRUSTED_DESC_NACL_DESC_FILE_INFO_H_
+
+#include "native_client/src/include/nacl_base.h"
+#include "native_client/src/public/nacl_file_info.h"
+
+EXTERN_C_BEGIN
+
+struct NaClDesc;
+struct NaClFileToken;
+
+/*
+ * NaClDescSetFileToken associates the contents of |token| with |desc|
+ * as NaClDesc metadata.  Any other metadata previously associated
+ * with |desc| is released / destroyed.  Returns non-zero value for
+ * success.  (Boolean function.)
+ */
+int NaClDescSetFileToken(struct NaClDesc *desc,
+                         struct NaClFileToken const *token);
+
+/*
+ * NaClDescGetFileToken checks if there is metadata associated with
+ * |desc| that contains a previously serialized NaClFileToken object.
+ * If so, it writes the NaClFileToken pointed to by |out_token| with
+ * the file token, and returns a non-zero value.  (Boolean function.)
+ */
+int NaClDescGetFileToken(struct NaClDesc *desc,
+                         struct NaClFileToken *out_token);
+
+EXTERN_C_END
+
+#endif