Summary:
This fix provides possibility to subscribe to a child animation lifecycle. You'll be able to observe every single animation:
```
Animated.sequence([
Animated.timing(
this.state.scale,
{
toValue: 0,
duration: 300,
onComplete: () => this.setState({someProp: 'new value'})
}
),
Animated.timing(
this.state.scale,
{
toValue: 1,
duration: 300
}
),
]).start();
```
`state.someProp`, will updated with `'new value'` when the first animation will be completed.
Closes https://github.com/facebook/react-native/pull/8494
Reviewed By: javache
Differential Revision: D3735322
Pulled By: foghina
fbshipit-source-id: fb69a4b993f7ab6a16da4fdd670e6c0b11c93517