[Service Offloading] Allow getDisplayMedia in non-secure context.

[Sunwoo-Nam]

In Service offloading, the android device gets contents for the webrtc server from the client device. The android device needs to use http protocol to access the client device, but getDisplayMedia does not work with http content. So, this patch allows that getDisplayMedia works on the http content by setting the document state to 'Secure'.