Missing React.StrictMode introduced in React 16.3

[NoMan2000]

Strict mode introduction.

https://reactjs.org/docs/strict-mode.html

Here's the proof. This could be a React issue or a Flow issue, but since the error is occurring in Flow, I'm opening it here.

https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVBLAtgBzgJwBcwAlAUwEMBjYqfOLMAcn0pqfSrgDsBnYgEYVeGKuWqEACvRxgAvGAAUOGbwCU8gHxLUASAA84mgDoAyoXyjCAWTgATMpt2owYfbzI0MPTS7C7nVwNgDy8fP1d9YCNCMwsrWwdfNSA

[georggrab]

There seems to already be a PR open for this: #6078
The Issue that is tracking adding the 16.3 Types can be found here: facebook/react#12553

For the time being, you can use $FlowFixMe as usual.

// $FlowFixMe: React Flow typings are not updated to React 16.3 yet
<React.StrictMode>
...
</React.StrictMode>