behaviour: Implement the implicit alpha parsing

ClutterBehaviour should implement the Scriptable interface
and parse ClutterAlpha when implicitly defined, instead of
having this ad hoc code inside ClutterScriptParser itself.

After all, only ClutterBehaviour supports Alpha defined
implicitly.

clutter/clutter-behaviour.c

@@ -71,12 +71,14 @@
 #include "config.h"
 #endif
 
-#include "clutter-main.h"
 #include "clutter-actor.h"
 #include "clutter-behaviour.h"
 #include "clutter-debug.h"
-#include "clutter-private.h"
+#include "clutter-main.h"
 #include "clutter-marshal.h"
+#include "clutter-private.h"
+#include "clutter-scriptable.h"
+#include "clutter-script-private.h"
 
 /**
  * clutter_knot_copy:
@@ -157,9 +159,13 @@ clutter_knot_get_type (void)
   return our_type;
 }
 
-G_DEFINE_ABSTRACT_TYPE (ClutterBehaviour,
-                        clutter_behaviour,
-                        G_TYPE_OBJECT);
+static void clutter_scriptable_iface_init (ClutterScriptableIface *iface);
+
+G_DEFINE_ABSTRACT_TYPE_WITH_CODE (ClutterBehaviour,
+                                  clutter_behaviour,
+                                  G_TYPE_OBJECT,
+                                  G_IMPLEMENT_INTERFACE (CLUTTER_TYPE_SCRIPTABLE,
+                                                         clutter_scriptable_iface_init));
 
 struct _ClutterBehaviourPrivate
 {
@@ -188,6 +194,36 @@ static guint behave_signals[LAST_SIGNAL] = { 0 };
                CLUTTER_TYPE_BEHAVIOUR,             \
                ClutterBehaviourPrivate))
 
+static gboolean
+clutter_behaviour_parse_custom_node (ClutterScriptable *scriptable,
+                                     ClutterScript     *script,
+                                     GValue            *value,
+                                     const gchar       *name,
+                                     JsonNode          *node)
+{
+  if (strncmp (name, "alpha", 5) == 0)
+    {
+      GObject *alpha;
+
+      alpha = _clutter_script_parse_alpha (script, node);
+      if (alpha != NULL)
+        {
+          g_value_init (value, CLUTTER_TYPE_ALPHA);
+          g_value_set_object (value, alpha);
+
+          return TRUE;
+        }
+    }
+
+  return FALSE;
+}
+
+static void
+clutter_scriptable_iface_init (ClutterScriptableIface *iface)
+{
+  iface->parse_custom_node = clutter_behaviour_parse_custom_node;
+}
+
 static void
 clutter_behaviour_dispose (GObject *gobject)
 {