gstreamer: Add Element::get_current_clock_time() and ::get_current_running_time()

This was added in GStreamer 1.18 but we can easily implement it
ourselves here for the time being and for older versions.

gstreamer/src/element.rs

@@ -265,6 +265,9 @@ pub trait ElementExtManual: 'static {
     where
         F: FnOnce(&Self) -> T + Send + 'static,
         T: Send + 'static;
+
+    fn get_current_running_time(&self) -> ::ClockTime;
+    fn get_current_clock_time(&self) -> ::ClockTime;
 }
 
 impl<O: IsA<Element>> ElementExtManual for O {
@@ -807,6 +810,26 @@ impl<O: IsA<Element>> ElementExtManual for O {
 
         Box::pin(receiver.map(|res| res.expect("sender dropped")))
     }
+
+    fn get_current_running_time(&self) -> ::ClockTime {
+        use ElementExt;
+
+        let base_time = self.get_base_time();
+        let clock_time = self.get_current_clock_time();
+
+        clock_time - base_time
+    }
+
+    fn get_current_clock_time(&self) -> ::ClockTime {
+        use ClockExt;
+        use ElementExt;
+
+        if let Some(clock) = self.get_clock() {
+            clock.get_time()
+        } else {
+            ::CLOCK_TIME_NONE
+        }
+    }
 }
 
 impl ElementClass {