Set file tokens for NaCl main nexe if available to enable validation caching.

ppapi/api/private/ppb_nacl_private.idl

 /* Copyright (c) 2012 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.
  */
 
 /* This file contains NaCl private interfaces. This interface is not versioned
  * and is for internal Chrome use. It may change without notice. */
 
 label Chrome {
   M25 = 1.0
@@ skipping 411 matching lines @@
   //   http://llvm.org/docs/CommandGuide/llc.html#cmdoption-mattr
   PP_Var GetCpuFeatureAttrs();
 
   /* Posts a message to the JavaScript object for the given instance.
    * This method may be called on any thread.
    */
   void PostMessageToJavaScript([in] PP_Instance instance,
                                [in] str_t message);
 
   /* Downloads the .nexe file at the given URL to a file, and sets |handle|
-   * to a handle to a file containing its contents. */
+   * to a handle to a file containing its contents.
+   * If metadata for identity-based validation caching is available
+   * then it sets file_token_lo and file_token_lo (otherwise left untouched).
+   */
   void DownloadNexe([in] PP_Instance instance,
                     [in] str_t url,
                     [out] PP_FileHandle handle,
+                    [out] uint64_t file_token_lo,
+                    [out] uint64_t file_token_hi,
                     [in] PP_CompletionCallback callback);
 };