PNaCl on-demand installs: Make a separate async IPC to check if PNaCl is installed

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. */
 
 #inline c
 #include "ppapi/c/private/pp_file_handle.h"
@@ skipping 61 matching lines @@
    * injection only to avoid the linkage problems that occur because the NaCl
    * plugin is built as a separate DLL/DSO
    * (see http://code.google.com/p/chromium/issues/detail?id=114439#c8).
    */
   int32_t BrokerDuplicateHandle([in] PP_FileHandle source_handle,
                                 [in] uint32_t process_id,
                                 [out] PP_FileHandle target_handle,
                                 [in] uint32_t desired_access,
                                 [in] uint32_t options);
 
+  /* Check if PNaCl is installed and attempt to install if necessary.
+   * Callback is called when the check is done and PNaCl is already installed,
+   * or after an on-demand install is attempted. Called back with PP_OK if
+   * PNaCl is available. Called back with an error otherwise.
+   */
+  int32_t EnsurePnaclInstalled([in] PP_Instance instance,
+                               [in] PP_CompletionCallback callback);
+
   /* Returns a read-only file descriptor of a file rooted in the Pnacl
    * component directory, or an invalid handle on failure.
-   * Do we want this to take a completion callback and be async, or
-   * could we make this happen on another thread?
    */
   PP_FileHandle GetReadonlyPnaclFd([in] str_t filename);
 
   /* This creates a temporary file that will be deleted by the time
    * the last handle is closed (or earlier on POSIX systems), and
    * returns a posix handle to that temporary file.
    */
   PP_FileHandle CreateTemporaryFile([in] PP_Instance instance);
 
   /* Create a temporary file, which will be deleted by the time the last
@@ skipping 42 matching lines @@
 
   /* Opens a NaCl executable file in the application's extension directory
    * corresponding to the file URL and returns a file descriptor, or an invalid
    * handle on failure. |metadata| is left unchanged on failure.
    */
   PP_FileHandle OpenNaClExecutable([in] PP_Instance instance,
                                    [in] str_t file_url,
                                    [out] uint64_t file_token_lo,
                                    [out] uint64_t file_token_hi);
 };