Refactor the process of choosing validators.

src/trusted/service_runtime/sel_main.c

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * NaCl Simple/secure ELF loader (NaCl SEL).
  */
 #include "native_client/src/include/portability.h"
@@ skipping 526 matching lines @@
     if (LOAD_OK != pq_error) {
       errcode = pq_error;
       nap->module_load_status = pq_error;
       fprintf(stderr, "Error while loading \"%s\": %s\n",
               NULL != nacl_file ? nacl_file
                                 : "(no file, to-be-supplied-via-RPC)",
               NaClErrorString(errcode));
     }
   }
 
-  nap->enable_dfa_validator = 0;
-  if (getenv("NACL_DANGEROUS_USE_DFA_VALIDATOR") != NULL) {
-    fprintf(stderr, "DANGER! USING THE UNSTABLE DFA VALIDATOR!\n");
-    nap->enable_dfa_validator = 1;
-  }
+  NaClSelectValidator(nap);
 
   /* Sanity check. */
   NaClSignalAssertNoHandlers();
 
   if (handle_signals) {
     NaClSignalHandlerInit();
   } else {
     /*
      * Patch the Windows exception dispatcher to be safe in the case
      * of faults inside x86-64 sandboxed code.  The sandbox is not
@@ skipping 350 matching lines @@
   fflush(stdout);
 
   if (handle_signals) NaClSignalHandlerFini();
   NaClAllModulesFini();
 
   NaClExit(ret_code);
 
   /* Unreachable, but having the return prevents a compiler error. */
   return ret_code;
 }