Hi, long time user, first time issuer.

I think I found a bug with the Profiler component. When I click on the `Save profile...` button at the top nothing happens and there appears to be no new files in my Downloads folder. I think it might be silently failing and that's why I am not getting any response.  Has anyone else ran into this issue?

Another thing I would like to mention is that I haven't looked through all of the documentation material about the new Profiler. I only read [this introductory blog post](https://reactjs.org/blog/2018/09/10/introducing-the-react-profiler.html), so if this issue is addressed elsewhere I apologize and also request the source to that solution.

Thank you for your time!

**Versions:**
 * `React DevTools 4.0.5`
 * `Firefox: 68.0.2(64-bit)`
 * `Ubuntu: 18.04`

// 
  const cloned = Object.assign([], hooks);
  const queue = [...cloned];
  while (queue.length > 0) {
    const current = queue.pop();
    // 
    delete current.id;
    delete current.isStateEditable;
    if (current.subHooks.length > 0) {
      queue.push(...current.subHooks);
    }
  }
  sanitize(cloned);
  try {
    return JSON.stringify(cloned, null, 2);
  } catch (error) {
    return '';
  }
}
// Keeping this in memory seems to be enough to enable the browser to download larger profiles.
// Without this, we would see a "Download failed: network error" failure.
let downloadUrl = null;
export function downloadFile(filename: string, text: string): void {