title: Duplicate request IDs in Puppeteer
body: <p>Chromium/Puppeteer <em>seems</em> to be reusing request IDs.</p>
  
  <p>I'm counting the requests and response IDs, I was expecting to get two of each ID (one on the request, then the same on on its <code>response.request()._requestId</code>) but I'm finding that there are more.</p>
  
  <p>I'm collecting the metrics with these two events:</p>
  
  <pre class="lang-js prettyprint-override"><code>    page.on('request', (request) =&gt; {
          const requestId = request._requestId;
          if (counter[requestId])
              counter[requestId]++;
          else
              counter[requestId.toString()] = 1;
      });
  
      page.on('response', (response) =&gt; {
  
          const requestId = response.request()._requestId;
  
          if (counter[requestId])
              counter[requestId]++;
          else
              counter[requestId] = 1;
      });
  </code></pre>
  
  <p>Results from stringifying the <code>counter</code> object:</p>
  
  <pre><code>{
      "750DF247357DA37DCCBE84ACEB1BB07E": 4,
      "22596.2": 2,
      "22596.3": 2,
      "22596.4": 2,
      "22596.5": 2,
      "22596.6": 2,
      "22596.7": 2,
      "22596.12": 2,
      "22596.13": 2,
      "22596.14": 2,
      "22596.19": 2,
      "22596.22": 2,
      "22596.35": 2,
      "22596.36": 2,
      "22596.37": 2,
      "22596.38": 2,
      "22596.39": 2,
      "22596.40": 2,
      "22596.41": 2,
      "22596.42": 2,
      "22596.43": 2,
      "22596.44": 2,
      "22596.45": 2,
      "22596.46": 2,
      "22596.47": 2,
      "22596.48": 2,
      "22596.49": 2,
      "22596.50": 6,
      "22596.51": 3,
      "22596.52": 3,
      "22596.53": 3,
      "22596.54": 3,
      "22596.55": 3,
      "22596.58": 2,
      "9D29F14302C8451741C1169CB32CDF21": 4,
      "581B16FB 5232782601F519C9558B218B": 4,
      "22596.60": 4,
      "22596.61": 2,
      "22596.62": 2,
      "22596.63": 2,
      "22596.65": 2,
      "22596.67": 2,
      "22596.68": 6,
      "22596.69": 2,
      "22596.70": 2,
      "22596.74": 2,
      "22596.76": 2,
      "22596.78": 2,
      "22596.79": 2,
      "22596.80": 2,
      "22596.86": 2,
      "22596.87": 2,
      "22596.88": 2,
      "22596. 89": 2,
      "22596.90": 2,
      "22596.91": 2,
      "22596.92": 2,
      "22596.93": 2,
      "22596.94": 2,
      "22596.95": 2,
      "22596.96": 2,
      "22596.97": 2,
      "817C68343178670A2608D3103FBBED3E": 4,
      "22596.98": 3,
      "22596.99": 2,
      "22596.100": 2,
  }
  </code></pre>
  
  <p>Is the <code>_requestId</code> supposed to be a unique number within the page?
  What </p>