Add a flag to LaunchSelLdr to skip grabbing a routing_id.

ppapi/api/private/ppb_nacl_private.idl

Index: ppapi/api/private/ppb_nacl_private.idl
diff --git a/ppapi/api/private/ppb_nacl_private.idl b/ppapi/api/private/ppb_nacl_private.idl
index 2dad7fe3f0bc3ce93e330b0adc7f1bd54909927c..60821c0df332e5089ebceaf5412af62718bd3a2e 100644
--- a/ppapi/api/private/ppb_nacl_private.idl
+++ b/ppapi/api/private/ppb_nacl_private.idl
@@ -31,10 +31,14 @@ interface PPB_NaCl_Private {
   /* Launches NaCl's sel_ldr process.  Returns PP_NACL_OK on success and writes
    * |socket_count| nacl::Handles to imc_handles. Returns PP_NACL_FAILED on
    * failure. The |enable_ppapi_dev| parameter controls whether GetInterface
-   * returns 'Dev' interfaces to the NaCl plugin.
+   * returns 'Dev' interfaces to the NaCl plugin.  The |uses_ppapi| flag
+   * indicates that the nexe run by sel_ldr will use the PPAPI APIs.
+   * This implies that LaunchSelLdr is run from the main thread.  If a nexe
+   * does not need PPAPI, then it can run off the main thread.
    */
   PP_NaClResult LaunchSelLdr([in] PP_Instance instance,
                              [in] str_t alleged_url,
+                             [in] PP_Bool uses_ppapi,
                              [in] PP_Bool enable_ppapi_dev,
                              [in] int32_t socket_count,
                              [out] mem_t imc_handles);