Emit signal when plugin latency changes

libs/ardour/ardour/latent.h

@@ -20,6 +20,8 @@
 #ifndef __ardour_latent_h__
 #define __ardour_latent_h__
 
+#include "pbd/signals.h"
+
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
 
@@ -76,6 +78,8 @@ public:
 		return _zero_latency;
 	}
 
+	PBD::Signal0<void> LatencyChanged;
+
 protected:
 	int  set_state (const XMLNode& node, int version);
 	void add_state (XMLNode*) const;

libs/ardour/plugin_insert.cc

@@ -3184,7 +3184,10 @@ PluginInsert::latency_changed ()
 {
 	// this is called in RT context, LatencyChanged is emitted after run()
 	_latency_changed = true;
-	// XXX This also needs a proper API not an owner() hack.
+	LatencyChanged (); /* EMIT SIGNAL */
+	// XXX This needs a proper API not an owner() hack:
+	// TODO Route should subscribe to LatencyChanged() and forward it
+	// to the session as processor_latency_changed.
 	assert (owner ());
 	static_cast<Route*>(owner ())->processor_latency_changed (); /* EMIT SIGNAL */
 }