[From the Profiler docs](https://reactjs.org/docs/profiler.html#onrender-callback):

> The Profiler requires an onRender function as a prop. React calls this function any time a component within the profiled tree “commits” an update.

However, given:

```jsx
import React from 'react'
import ReactDOM from 'react-dom'

function Counter() {
  const [count, setCount] = React.useState(0)
  const increment = () => setCount(c => c + 1)
  return <button onClick={increment}>{count}</button>
}

function App() {
  return (
    <div>
      <React.Profiler
        id="counter"
        onRender={() => console.log('called')}
      >
        <div>
          Profiled counter
          <Counter />
        </div>
      </React.Profiler>
      <div>
        Unprofiled counter
        <Counter />
      </div>
    </div>
  )
}

ReactDOM.render(<App />, document.getElementById('root'))
```

I'm getting a log when I click on the unprofiled counter.

Reproduction: https://codesandbox.io/s/react-codesandbox-tnff6

Am I misunderstanding this API, or is this a bug?
if (Component) {
    warningWithoutStack(
      !Component.childContextTypes,
      '%s(...): childContextTypes cannot be defined on a function component.',
      Component.displayName || Component.name || 'Component',
    );
  }
  if (workInProgress.ref !== null) {
    let info = '';
    const ownerName = getCurrentFiberOwnerNameInDevOrNull();
    if (ownerName) {
      info += '\n\nCheck the render method of `' + ownerName + '`.';
    }
    let warningKey = ownerName || workInProgress._debugID || '';
    const debugSource = workInProgress._debugSource;
    if (debugSource) {
      warningKey = debugSource.fileName + ':' + debugSource.lineNumber;
    }
    if (!didWarnAboutFunctionRefs[warningKey]) {
      didWarnAboutFunctionRefs[warningKey] = true;
      warning(
        false,
        'Function components cannot be given refs. ' +
          'Attempts to access this ref will fail. ' +
          'Did you mean to use React.forwardRef()?%s',
        info,
      );
    }
  }
  if (