Add missing file

gstreamer-webrtc/src/web_r_t_c_session_description.rs

+// Copyright (C) 2018 Sebastian Dröge <sebastian@centricular.com>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use WebRTCSDPType;
+use WebRTCSessionDescription;
+use ffi;
+use glib::translate::*;
+use gst_sdp;
+use std::mem;
+
+impl WebRTCSessionDescription {
+    pub fn new(type_: WebRTCSDPType, mut sdp: gst_sdp::SDPMessage) -> WebRTCSessionDescription {
+        assert_initialized_main_thread!();
+        unsafe {
+            let desc = from_glib_full(ffi::gst_webrtc_session_description_new(
+                type_.to_glib(),
+                sdp.to_glib_none_mut().0,
+            ));
+            mem::forget(sdp);
+            desc
+        }
+    }
+}