add a new update() method to PBD::TimingStats to allow use of an already-computed interval

libs/pbd/pbd/timing.h

@@ -83,6 +83,10 @@ public:
 	void update () {
 		m_last_val = g_get_monotonic_time ();
 	}
+	void update (uint64_t interval) {
+		m_start_val = 0;
+		m_last_val = interval;
+	}
 
 	void reset () {
 		m_start_val = m_last_val = 0;
@@ -134,6 +138,17 @@ public:
 		}
 	}
 
+	/* interval computed externally */
+	void update (uint64_t interval)
+	{
+		/* throw away the first 1000 values */
+		if (_update_cnt++ < 1000) {
+			return;
+		}
+		Timing::update (interval);
+		calc ();
+	}
+
 	void reset ()
 	{
 		Timing::reset ();