feat(chromium): roll Chromium to r609904 (#3587)

This roll includes:
- https://crrev.com/609886 - DevTools: force-detach worker sessions
  on navigation

This should eliminate flakiness with our worker test.

package.json

@@ -8,7 +8,7 @@
     "node": ">=6.4.0"
   },
   "puppeteer": {
-    "chromium_revision": "608752"
+    "chromium_revision": "609904"
   },
   "scripts": {
     "unit": "node test/test.js",