58.0.3027.0, but it's broken on 56 and 57 too, and most likely it's been broken since 34 (See  crbug.com/350445 ).

The 'load' event is dispatched few minutes too late, or until the next relayout. Such relayout may never happen when loading in background page in NaCl module. We do that in two component extensions: Image Loader and ZIP unpacker.

Note, that the load event works if the NaCl module is loaded in the global scope of the background page. However, loading the NaCl event in any event handler, such as onLaunched fails.

This became visible now, as we try to defer loading a NaCl module, or unload and reload when needed in order to fix  crbug.com/517741 .

We do a workaround suggested by  crbug.com/350445  few years ago and it somehow works, but this is terribly broken, and should get fixed. With the hack loading a module takes less than a second. Without the hack, takes minutes.