title: Debounce search filter
body: <p>I'm trying to debounce my search function but I get an error.
  I have an ember search input and this in my array controller:</p>
  
  <pre><code>App.PostsController = Ember.ArrayController.extend({
      watchSearch: function() {
        Em.run.debounce(this, this.itemsa, 400);
      }.observes("search"),
  
      itemsa: function() {
        var searched = this.get("search") ? this.get("searchedItems") : this;
        return searched;    
      }.property("searchedItems"),
  
    searchedItems: function() {
      var search = this.get('search').toLowerCase();
      return this.filter(function(item) {
        return item.get('title').toLowerCase().indexOf(search) != -1;
      })
    }.property('search', 'title')
  });
  </code></pre>
  
  <p>And in my template I have:</p>
  
  <pre><code>&lt;script type="text/x-handlebars" id="posts"&gt;
    {{#each itemsa}}
      {{title}}
    {{/each}}
  &lt;/script&gt;
  </code></pre>