Update more extension manifests to manifest_version 2

chrome/test/data/extensions/allow_silent_upgrade/hosts6_new.json

 {
   "name": "allow silent update",
   "version": "1.0",
+  "manifest_version": 2,
   "permissions": [
     "tabs",
     "notifications",
     "http://*.example.com/"
   ],
   "content_scripts": [
     {
       "matches": [
         "http://*.example.com/*",
         "http://*.example.co.uk/*",
         "https://*.example.com.au/*"
       ],
       "js": ["404.js"]
     }
   ]
 }