Provide chrome the option of learning the debug stub port chosen by nacl.

src/public/chrome_main.h

Index: src/public/chrome_main.h
diff --git a/src/public/chrome_main.h b/src/public/chrome_main.h
index afa70b42cc11a78621b404f08b2357883356a579..d8f387efb7f242ddef9e12c9c9a6df68079b90af 100644
--- a/src/public/chrome_main.h
+++ b/src/public/chrome_main.h
@@ -101,6 +101,11 @@ struct NaClChromeMainArgs {
 #endif
 
   /*
+   * Callback called when debug stub port is known.  Optional; may be NULL.
+   */
+  void (*debug_stub_server_port_selected_handler_func)(uint16_t port);
+
+  /*
    * Callback to use for creating shared memory objects.  Optional;
    * may be NULL.
    */