Summary:
In the context of an app an image exists in three resolutions on the server: `thumb` (30px) `feed` (300px) `full` (900px). When looking at an individual item a user can come either from the feed, via a permalink or from other parts of the app. This allows a situation where the `feed` image might or might not already be loaded somewhere in the app. In the detail view I want to render `thumb` with a blur (to quickly display something), then the `feed` image if it exists to have something decent to display until `full` loads. However it is quite a waste to load the `feed` image if it isn't already in cache, and will slow down the time until `full` is loaded. It is possible to track the navigation from feed->detail and that the `feed` image has actually completed loading by the feed component however as component hierarchies grow this turns into quite a lot of prop passing and bad separation of concerns.
NSURLRequests accepts a [Cache Policy](https://developer.apple.com/reference/fo
Closes https://github.com/facebook/react-native/pull/10844
Differential Revision: D4425959
Pulled By: lacker
fbshipit-source-id: 679835439c761a2fc894f56eb6d744c036cf0b49
52d8851fc8
