Introduce pattern for cleaner transition to background

[SamSaffron]

Per: http://stackoverflow.com/a/10319761/17174

When app transitions to background native blob should provide the hooks to extend execution until all downloads are complete (or properly timed out)

[wkh237]

@SamSaffron , Thanks for your information, I think this is a very improtant feature, and we've tried to implent background transmission mechanism, but it's not an easy task, perhaps still need some time.

[SamSaffron]

Recently I have been fighting super hard to get background fetch going. It seems discourse/DiscourseMobile@989c3a3 may have done the trick but it took me days of debugging and I am still not certain.

Cleanly dealing with transition to background is a great feature for RN to have, I will raise a separate ticket so core react networking networking deals with this as well

[wkh237]

Yeah, I'm agree with you. On Android, developer can use Download Manager but there's no such a solution on IOS.

It would be great to have this implemented, I'll look into it 👍

[SamSaffron]

I also opened this issue now to see if core should add something facebook/react-native#9678

[wkh237]

related #141

[wkh237]

@SamSaffron , I've added fetch.expire() API so that you can handle expired request. Please try upgrade 0.10.0-beta.5 from npm if needed, thank you 😄

Document and example