## Details
Using version 4.0.2 (8/15/2019) I am getting a maximum call stack size exceeded when my app starts up. While my app using this is a little different I have replicated the issue using a fresh create-react-app. I will include the App.js code below.

## Steps to reproduce
1. Create a new app using version 3.0.1 of create-react-app
2. Replace the code in App.js with the code listed below
3. Inspect the console, there should be a stack trace from a maximum call stack exceeded error

## App.js
```
import React from 'react';
import logo from './logo.svg';
import './App.css';

const createDivs = num => {
    const rtn = [];
    for(let i = 0; i < num; i++) {
        const key = `div-${i}`;
        rtn.push(<div className={key} key={key} />)
    }
    return rtn;
}

function App() {
  return (
    <div className="App">
      <header className="App-header">
        <img src={logo} className="App-logo" alt="logo" />
        <p>
          Edit <code>src/App.js</code> and save to reload.
        </p>
        <a
          className="App-link"
          href="https://reactjs.org"
          target="_blank"
          rel="noopener noreferrer"
        >
          Learn React
        </a>
      </header>
      <div>
        {createDivs(15000)}
      </div>
    </div>
  );
}

export default App;
```

## Call Stack
<details>

<summary>backend.js:formatted:2097 Uncaught RangeError: Maximum call stack size exceeded
</summary>

```
    at ge (backend.js:formatted:2097)
    at Ge (backend.js:formatted:2435)
    at Ge (backend.js:formatted:2478)
    at Ge (backend.js:formatted:2478)
    at Ge (backend.js:formatted:2478)
    at Ge (backend.js:formatted:2478)
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    at Ge (backend.js:formatted:2478)
ge @ backend.js:formatted:2097
Ge @ backend.js:formatted:2435
Ge @ backend.js:formatted:2478
Ge @ backend.js:formatted:2478
Ge @ backend.js:formatted:2478
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postMessage (async)
r @ contentScript.js:1
88 @ contentScript.js:1
n @ contentScript.js:1
(anonymous) @ contentScript.js:1
(anonymous) @ contentScript.js:1
Show 170 more frames
```

</details>

This was not an issue in the previous version of react-devtools.
case PROFILER_NUMBER:
          case PROFILER_SYMBOL_STRING:
            return ElementTypeProfiler;
          default:
            return ElementTypeOtherOrUnknown;
        }
    }
  }
   This is a slightly annoying indirection.
   It is currently necessary because DevTools wants to use unique objects as keys for instances.
   However fibers have two versions.
   We use this set to remember first encountered fiber for each conceptual instance.
  function getPrimaryFiber(fiber: Fiber): Fiber {
    if (primaryFibers.has(fiber)) {
      return fiber;
    }
    const {alternate} = fiber;
    if (alternate != null && primaryFibers.has(alternate)) {
      return alternate;
    }
    primaryFibers.add(fiber);
    return fiber;
  }
  const fiberToIDMap: Map<Fiber, number> = new Map();
  const idToFiberMap: Map<number, Fiber> = new Map();
  const primaryFibers: Set<Fiber> = new Set();
   When profiling is supported, we store the latest tree base durations for each Fiber.
   This is so that we can quickly capture a snapshot of those values if profiling starts.
   If we didn't store these values, we'd have to crawl the tree when profiling started,
   and use a slow path to find each of the current Fibers.