tray: Show warning in network tray when VPN or proxy used.

ash/system/networking_config_delegate.h

Index: ash/system/networking_config_delegate.h
diff --git a/ash/system/networking_config_delegate.h b/ash/system/networking_config_delegate.h
index b040e70e291cf3a18b8d8f159cc433428f2fe8df..4e7f890d2f46904ce04d68542074ef52bff1aea6 100644
--- a/ash/system/networking_config_delegate.h
+++ b/ash/system/networking_config_delegate.h
@@ -38,6 +38,8 @@ class NetworkingConfigDelegate {
   virtual std::unique_ptr<const ExtensionInfo> LookUpExtensionForNetwork(
       const std::string& guid) = 0;
 
+  virtual bool HasDefaultNetworkProxyConfigured() = 0;
+
  private:
   DISALLOW_ASSIGN(NetworkingConfigDelegate);
 };