add Editor::default_time_domain()

Not 100% certain about the logic here, but at least the method exists now

gtk2_ardour/editor.cc

@@ -6410,3 +6410,13 @@ Editor::duration_to_pixels_unrounded (timecnt_t const & dur) const
 {
 	return sample_to_pixel_unrounded (dur.samples());
 }
+
+Temporal::TimeDomain
+Editor::default_time_domain () const
+{
+	if (_grid_type == GridTypeNone || _snap_mode == SnapOff) {
+		return AudioTime;
+	}
+
+	return BeatTime;
+}

gtk2_ardour/editor.h

@@ -168,6 +168,8 @@ public:
 
 	bool pending_locate_request() const { return _pending_locate_request; }
 
+	Temporal::TimeDomain default_time_domain() const;
+
 	samplepos_t leftmost_sample() const { return _leftmost_sample; }
 
 	samplecnt_t current_page_samples() const {

gtk2_ardour/public_editor.h

@@ -130,6 +130,11 @@ public:
 
 	virtual void setup_tooltips() = 0;
 
+	/* returns the time domain to be used when there's no other overriding
+	 * reason to choose one.
+	 */
+	virtual Temporal::TimeDomain default_time_domain() const = 0;
+
 	/** Attach this editor to a Session.
 	 * @param s Session to connect to.
 	 */