title: Don't raise TextChanged while continuous typing
body: <p>I have a textbox that has a fairly hefty <code>_TextChanged</code> event handler. Under normal typing condition the performance is okay, but it can noticeably lag when the user performs a long continuous action, such as keeping the backspace button pressed to delete a lot of text at once.</p>
  
  <p>For example, the event took 0.2 seconds to complete, but the user is performing one deletion every 0.1 seconds. Thus, it cannot catch up and there will be a backlog of events that needs to be handled, leading to the UI lagging.</p>
  
  <p>However, the event does not need to run for these in-between states, because it only cares about the end result. Is there any way to let the event handler know that it should process only the latest event, and ignore all the previous stale changes?</p>