When a #GstTestClock is constructed it will have a certain start time set.
If the clock was created using gst_test_clock_new_with_start_time() then
this property contains the value of the start_time argument. If
gst_test_clock_new() was called the clock started at time zero, and thus
this property contains the value 0.
The parent of the object. Please note, that when changing the 'parent' property, we don't emit #GObject::notify and #GstObject::deep-notify signals due to locking issues. In some cases one can use #GstBin::element-added or #GstBin::element-removed signals on the parent to achieve a similar effect.