screen-cast-session: Add window-id support

Use the "window-id" property to select the window to cast using
RecordWindow.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/306
(cherry picked from commit c786b6c13c)

src/backends/meta-screen-cast-session.c

@@ -340,6 +340,7 @@ handle_record_window (MetaDBusScreenCastSession *skeleton,
   MetaWindow *window;
   GError *error = NULL;
   MetaDisplay *display;
+  GVariant *window_id_variant = NULL;
   MetaScreenCastWindowStream *window_stream;
   MetaScreenCastStream *stream;
   char *stream_path;
@@ -352,8 +353,24 @@ handle_record_window (MetaDBusScreenCastSession *skeleton,
       return TRUE;
     }
 
+  if (properties_variant)
+    window_id_variant = g_variant_lookup_value (properties_variant,
+                                                "window-id",
+                                                G_VARIANT_TYPE ("t"));
+
   display = meta_get_display ();
-  window = meta_display_get_focus_window (display);
+  if (window_id_variant)
+    {
+      uint64_t window_id;
+
+      g_variant_get (window_id_variant, "t", &window_id);
+      window = meta_display_get_window_from_id (display, window_id);
+    }
+  else
+    {
+      window = meta_display_get_focus_window (display);
+    }
+
   if (!window)
     {
       g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,

src/org.gnome.Mutter.ScreenCast.xml

@@ -86,7 +86,10 @@
 
 	Record a single window.
 
-	Available @properties include: (none)
+	Available @properties include:
+
+	* "window-id" (t): Id of the window to record.
+
     -->
     <method name="RecordWindow">
       <arg name="properties" type="a{sv}" direction="in" />