GetHelp: Add missing permission "metricsPrivate" in manifest.json

chrome/browser/resources/chromeos/genius_app/manifest.json

 {
   "key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDNAtiHknM7LHSwE9YKiFFvYvsp0TkfIriWfrjz53odJD0jEbOtyNhVXqdBOdtcenbSraxt7oJ9GlIfUkvBMP5iOpcrJkYfuNJv8ANHTKC79TjGXRg76TjiqpNI+R2NiVav1pXlzYZpu0ToaiaOcr3IgoGsvIUPcC6pd1U5AjdrCQIDAQAB",
   "manifest_version": 2,
   "name": "__MSG_app_name__",
   "description": "__MSG_app_description__",
   "version": "0.2",
   "minimum_chrome_version": "28",
   "default_locale": "en",
   "incognito" : "split",
   "icons": {
     "16": "icon/16.png",
     "32": "icon/32.png",
     "48": "icon/48.png",
     "64": "icon/64.png",
     "96": "icon/96.png",
     "128": "icon/128.png",
     "256": "icon/256.png"
   },
   "app": {
     "background": {
       "persistent": false,
       "page": "background.html"
     }
   },
   "permissions": [
     "identity",
     "chromeosInfoPrivate",
     "firstRunPrivate",
     "management",
+    "metricsPrivate",
     "webview",
     "storage",
     "unlimitedStorage",
     "https://*.ytimg.com/*",
     "https://www.google.com/*",
     "https://commondatastorage.googleapis.com/*",
     "https://storage.googleapis.com/*",
     "https://www-googleapis-test.sandbox.google.com/*",
     "https://www.googleapis.com/*",
     "https://www.google-analytics.com/"
@@ skipping 15 matching lines @@
     },
     "home": {
       "matches": [
         "https://support.google.com/chromeos-gethelp",
         "https://support.google.com/chromeos-gethelp/"
       ],
       "title": "Open Help"
     }
   }
 }