Check that the PNaCl cache hash is truly derived from the bitcode content.

ppapi/c/private/ppb_nacl_hash_private.h

+/* Copyright (c) 2013 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* From private/ppb_nacl_hash_private.idl modified Wed May  1 11:04:31 2013. */
+
+#ifndef PPAPI_C_PRIVATE_PPB_NACL_HASH_PRIVATE_H_
+#define PPAPI_C_PRIVATE_PPB_NACL_HASH_PRIVATE_H_
+
+#include "ppapi/c/pp_bool.h"
+#include "ppapi/c/pp_macros.h"
+#include "ppapi/c/pp_stdint.h"
+
+#define PPB_NACL_HASH_PRIVATE_INTERFACE_1_0 "PPB_NaCl_Hash_Private;1.0"
+#define PPB_NACL_HASH_PRIVATE_INTERFACE PPB_NACL_HASH_PRIVATE_INTERFACE_1_0
+
+/**
+ * @file
+ * This file contains NaCl private interfaces for hashing. This interface
+ * is not versioned and is for internal Chrome use. It may change without
+ * notice. If we convert the NaCl plugin from PPAPI to be renderer code
+ * then we can depend on the chrome hash functions directly.
+ */
+
+
+/**
+ * @addtogroup Interfaces
+ * @{
+ */
+/* PPB_NaCl_Hash_Private */
+struct PPB_NaCl_Hash_Private_1_0 {
+  /* Create a hasher object for incremental hashing. */
+  void* (*CreateSHA256Hasher)(void);
+  /* Update the hash with len more bytes of data. */
+  void (*Update)(void* hasher, const void* data, uint32_t len);
+  /* Finish hashing and get a digest up to len bytes. */
+  void (*Finish)(void* hasher, void* output, uint32_t len);
+  /* Delete the hasher object. */
+  void (*Delete)(const void* hasher);
+  /* Compare two hashes and return PP_TRUE if they are equal. */
+  PP_Bool (*SecureMemEqual)(const void* hash1, const void* hash2, uint32_t len);
+};
+
+typedef struct PPB_NaCl_Hash_Private_1_0 PPB_NaCl_Hash_Private;
+/**
+ * @}
+ */
+
+#endif  /* PPAPI_C_PRIVATE_PPB_NACL_HASH_PRIVATE_H_ */
+