screen-cast-session: Add screen-cast window mode

Window mode will cast the content of a single window using the
`MetaScreenCastWindow` interface.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/306

src/backends/meta-screen-cast-window-stream-src.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2018 Red Hat Inc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ *
+ */
+
+#ifndef META_SCREEN_CAST_WINDOW_STREAM_SRC_H
+#define META_SCREEN_CAST_WINDOW_STREAM_SRC_H
+
+#include "backends/meta-screen-cast-stream-src.h"
+
+typedef struct _MetaScreenCastWindowStream MetaScreenCastWindowStream;
+
+#define META_TYPE_SCREEN_CAST_WINDOW_STREAM_SRC (meta_screen_cast_window_stream_src_get_type ())
+G_DECLARE_FINAL_TYPE (MetaScreenCastWindowStreamSrc,
+                      meta_screen_cast_window_stream_src,
+                      META, SCREEN_CAST_WINDOW_STREAM_SRC,
+                      MetaScreenCastStreamSrc)
+
+MetaScreenCastWindowStreamSrc * meta_screen_cast_window_stream_src_new (MetaScreenCastWindowStream  *window_stream,
+                                                                        GError                     **error);
+
+#endif /* META_SCREEN_CAST_WINDOW_STREAM_SRC_H */