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

Index: src/native_client/src/trusted/service_runtime/sel_main_chrome.c
diff --git a/src/native_client/src/trusted/service_runtime/sel_main_chrome.c b/src/native_client/src/trusted/service_runtime/sel_main_chrome.c
index e1fc3c7830797a90414c74d37067179533726b61..94ec25197842c5443ac964169b146d3f937e1ee4 100644
--- a/src/native_client/src/trusted/service_runtime/sel_main_chrome.c
+++ b/src/native_client/src/trusted/service_runtime/sel_main_chrome.c
@@ -105,12 +105,14 @@ int NaClMainForChromium(int handle_count, const NaClHandle *handles,
     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);