Display correct error message when the client fails to establish P2P connection.

remoting/webapp/_locales/en/messages.json

 {
   "ACCESS_CODE": {
     "message": "Access code",
     "description": "Label for the access code entry box. This is where the client user enters the code that permits access to the host."
   },
   "ACCESS_CODE_TIMER": {
     "message": "This access code will expire in $timeout$",
     "description": "Text displayed when the access code is due to time out within 30 seconds.",
     "placeholders": {
       "timeout": {
@@ skipping 93 matching lines @@
     "description": "Error that is shown on the client side when we don't get a response from the host."
   },
   "ERROR_INCOMPATIBLE_PROTOCOL": {
     "message": "An incompatible version of Chromoting was detected. Please make sure that you have the latest version of Chromium and Chromoting on both computers and try again.",
     "description": "Error that is shown on the client side when incompatible Chromoting versions are installed on host and client."
   },
   "ERROR_INVALID_ACCESS_CODE": {
     "message": "The access code is invalid. Please try again.",
     "description": "Error displayed if an invalid access code is entered."
   },
+  "ERROR_NETWORK_FAILURE": {
+    "message": "Unable to reach the host. This is probably due to the configuration of the network you are using.",
+    "description": "Error displayed when the host is online, but we are unable to connect to it due to network configuration."
+  },
   "ERROR_MISSING_PLUGIN": {
     "message": "Some components required for Chromoting are missing. Please make sure you're running the latest version of Chromium and try again.",
     "description": "Error displayed if the client plugin fails to load."
   },
   "ERROR_NO_RESPONSE": {
     "message": "The server failed to respond to the network request.",
     "description": "Error displayed by the client if the server does not respond to a network request."
   },
   "ERROR_SERVICE_UNAVAILABLE": {
     "message": "The service is temporarily unavailable. Please try again later.",
@@ skipping 151 matching lines @@
   },
   "TOOLTIP_RENAME": {
     "message": "Edit computer name",
     "description": "The tool-tip shown when the user hovers over the 'rename host' button. Clicking this button allows the host name to be edited in-place."
   },
   "WARNING_NAT_DISABLED": {
     "message": "NOTE: Policy settings permit connections only between computers within your network.",
     "description": "Message displayed at the bottom of the host screen if local policy dictates that NAT traversal is disabled, meaning that connections outside the local network will not work."
   }
 }