Add an IPC channel between the NaCl loader process and the renderer.

ppapi/api/private/finish_writing_these/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. */
 
 /* PPB_NaCl_Private */
 interface PPB_NaCl_Private_0_2 {
   /* This function launches NaCl's sel_ldr process.  On success, the function
    * returns true, otherwise it returns false.  When it returns true, it will
    * write |socket_count| nacl::Handles to imc_handles and will write the
    * nacl::Handle of the created process to |nacl_process_handle|.  Finally,
    * the function will write the process ID of the created process to
    * |nacl_process_id|.
    */
   bool LaunchSelLdr(
+      [in] int32_t instance,
       [in] str_t alleged_url,
       [in] int32_t socket_count,
       [out] mem_t imc_handles,
       [out] mem_t nacl_process_handle,
       [out] int32_t nacl_process_id);
 
   /* On POSIX systems, this function returns the file descriptor of
    * /dev/urandom.  On non-POSIX systems, this function returns 0.
    */
   int32_t UrandomFD();
 
   /* Whether the Pepper 3D interfaces should be disabled in the NaCl PPAPI
    * proxy. This is so paranoid admins can effectively prevent untrusted shader
    * code to be processed by the graphics stack.
    */
   bool Are3DInterfacesDisabled();
 };