Real-user measurements skip automated browsers (navigator.webdriver, crawler and headless user agents, checked in the page only): the first samples were our own headless test runs (FCP 180 ms) (#223)

ddiff --git a/public/js/ov-rum.js b/public/js/ov-rum.js
iindex 6da485d2..8c08f50c 100644
---- a/public/js/ov-rum.js
++++ b/public/js/ov-rum.js
@@@ -6,6 +6,9 @@
  (function () {
      'use strict';
      if (!('PerformanceObserver' in window) || !navigator.sendBeacon) return;
++    // Automated browsers are not visitors: crawlers that run scripts, headless test runs (ours included). Checked here
++    // only; the user agent is never sent.
++    if (navigator.webdriver || /bot|crawl|spider|slurp|headless|lighthouse|pagespeed|preview|phantom|puppeteer|playwright/i.test(navigator.userAgent || '')) return;
      const m = { fcp: 0, lcp: 0, cls: 0, inp: 0, tbt: 0, errs: [] };
      const watch = (type, fn, extra) => {
          try { new PerformanceObserver((list) => list.getEntries().forEach(fn)).observe(Object.assign({ type, buffered: true }, extra)); } catch (e) { /* not in this browser */ }
ddiff --git a/test/rum.test.js b/test/rum.test.js
iindex 824703ef..be6829ec 100644
---- a/test/rum.test.js
++++ b/test/rum.test.js
@@@ -80,7 +80,9 @@ const { createRum, pageKind, deviceClass } = require('../server/web/rum');
      const app_js = fs.readFileSync(path.join(__dirname, '../public/js/app.js'), 'utf8');
      assert.ok(app_js.includes("if (Math.random() < 0.25 && window.ov) (window.requestIdleCallback || setTimeout)(() => ov.loadScript('/js/ov-rum.js'));"));
      const client = fs.readFileSync(path.join(__dirname, '../public/js/ov-rum.js'), 'utf8');
--    assert.ok(client.includes("navigator.sendBeacon('/api/rum'") && !/cookie|localStorage|userAgent/i.test(client.replace(/\/\*[\s\S]*?\*\//g, '')), 'the beacon carries no identifier');
++    assert.ok(client.includes("navigator.sendBeacon('/api/rum'") && !/cookie|localStorage/i.test(client.replace(/\/\*[\s\S]*?\*\//g, '')), 'the beacon carries no identifier');
++    assert.ok(/navigator\.webdriver \|\| \/bot\|crawl\|spider[^/]*headless/.test(client), 'automated browsers (crawlers, headless runs) send nothing');
++    assert.ok(!/userAgent[^)]*sendBeacon|JSON\.stringify\(\{[^}]*userAgent/.test(client), 'the user agent is checked, never sent');
  
      console.log('rum: all checks passed');
  })().catch((e) => { console.error(e); process.exit(1); });