Summary:
This is a follow up of the work by brentvatne in #5052. This addresses the feedback by astreet.
- Uses ReactChoreographer with a new callback type
- Callback dispatch logic moved to JS
- Only calls into JS when needed, when there are pending callbacks, it even removes the Choreographer listener when no JS context listen for idle events.
** Test plan **
Tested by running a background task that burns all remaining idle time (see new UIExplorer example) and made sure that UI and JS fps stayed near 60 on a real device (Nexus 6) with dev mode disabled. Also tried adding a JS driven animation and it stayed smooth.
Tested that native only calls into JS when there are pending idle callbacks.
Also tested that timers are executed before idle callback.
```
requestIdleCallback(() => console.log(1));
setTimeout(() => console.log(2), 100);
burnCPU(1000);
// 2
// 1
```
I did *not* test with webworkers but it should work as I'm using executor tokens.
Closes https://github.com/facebook/react-native/pull/8569
Differential Revision: D3558869
Pulled By: astreet
fbshipit-source-id: 61fa82eb26001d2b8c2ea69c35bf3eb5ce5454ba
Janic Duplessis
Gabe Levi
Jeff Morrison