[Chromoting] Add socket permission to AppRemoting manifest.

remoting/webapp/app_remoting/manifest_common.json.jinja2

   {{ MANIFEST_KEY_FOR_UNOFFICIAL_BUILD }}
   "name": "{{APP_NAME}}",
   "description": "{{APP_DESCRIPTION}}",
   "version": "{{ FULL_APP_VERSION }}",
   "manifest_version": 2,
   "default_locale": "en",
   "app": {
     "background": {
       "scripts": ["ar_background.js", "platform.js"]
     }
@@ skipping 15 matching lines @@
     "app.window.shape",
     "clipboardRead",
     "clipboardWrite",
     "contextMenus",
     "experimental",
     "fileSystem",
     "fullscreen",
     "https://relay.google.com/*",
     "identity",
     "pointerLock",
-    "storage"
+    "storage",
+    {
+      "socket": [
+        "tcp-connect",
+        "tcp-listen",
+        "udp-send-to",
+        "udp-bind",
+        "udp-multicast-membership",
+        "resolve-host",
+        "network-state"
+      ]
+    }
   ],
   "oauth2": {
     "client_id": "{{ REMOTING_IDENTITY_API_CLIENT_ID }}",
     "scopes": [
       "https://www.googleapis.com/auth/appremoting.runapplication https://www.googleapis.com/auth/googletalk https://www.googleapis.com/auth/userinfo#email https://www.googleapis.com/auth/userinfo.profile https://docs.google.com/feeds/ https://www.googleapis.com/auth/drive"
     ]
   },
   "sandbox": {
     "pages": [ "wcs_sandbox.html" ]
   }