Summary:
1. Using weak container to hold the currently opened alerts.
2. Using weak reference to alertController in action handler block.
3. BTW, remove the unused vars: _alertCallbacks, _alertButtonKeys.
Test plan (required)
```
- (void)invalidate
{
for (UIAlertController *alertController in _alertControllers) {
[alertController.presentingViewController dismissViewControllerAnimated:YES completion:nil];
}
}
```
Since we use weak container, _alertControllers should only contains the currently opened alerts.
I test this way: Put a breakpoint in invalidate, open the UIExplorer play with the 'Alert' & 'AlertIOS' examples, then fire a reload and see if _alertControllers contains the expected values.
Closes https://github.com/facebook/react-native/pull/10407
Differential Revision: D4078649
Pulled By: lacker
fbshipit-source-id: 8509e7e7142379a81d5b28c9067c085bad8bb5cb