Add an assertion to check that Chrome/Breakpad does not install a signal handler

src/native_client/src/trusted/service_runtime/sel_main_chrome.c

 /*
  * Copyright (c) 2011 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.
  */
 
 #include "native_client/src/include/portability.h"
 #include "native_client/src/include/portability_io.h"
 
 #if NACL_OSX
@@ skipping 87 matching lines @@
    * We enable the signal handler to verify properties of the platform such
    * as the ability to trap a page on execute.
    */
   NaClSignalHandlerInit();
   errcode = NaClRunSelQualificationTests();
   if (LOAD_OK != errcode) {
     nap->module_load_status = errcode;
     fprintf(stderr, "Error while loading in SelMain: %s\n",
             NaClErrorString(errcode));
   }
+  /* Remove the handler that was used for platform qualification tests. */
+  NaClSignalHandlerFini();
 
   /*
-   * Remove the handler and let error pass to Chrome's handlers.
+   * Check that Chrome did not register any signal handlers, because
+   * these are not always safe.
    */
-  NaClSignalHandlerFini();
-
+  NaClSignalAssertNoHandlers();
 
   /* Give debuggers a well known point at which xlate_base is known.  */
   NaClGdbHook(&state);
 
   /*
    * If export_addr_to is set to a non-negative integer, we create a
    * bound socket and socket address pair and bind the former to
    * descriptor 3 and the latter to descriptor 4.  The socket address
    * is written out to the export_addr_to descriptor.
    *
@@ skipping 68 matching lines @@
    */
   return ret_code;
 
  done:
   fflush(stdout);
 
   NaClAllModulesFini();
 
   return ret_code;
 }