title: Can't display sub-menu for custom ActionProvider
body: <p>I've created a custom <code>ActionProvider</code> that I want to use to show a sub-menu for sorting, similar visually to <code>ShareActionProvider</code>. The action view displays as expected, but clicking on the icon doesn't display the sub-menu or show any visual feedback (pressed state) at all. I'm using the support v7 library for backward compatibility action bar. Is there an implementation I am missing to display the menu?</p>
  
  <p>ActionProvider:</p>
  
  <pre><code>public class SortActionProvider extends ActionProvider implements OnMenuItemClickListener {
  
      private Context mContext;
  
      public SortActionProvider(Context context) {
          super(context);
          mContext = context;
      }
  
      @Override
      public View onCreateActionView(){
          ImageView imageView = new ImageView(mContext);
          imageView.setImageResource(R.drawable.ic_action_sort_by_size);
  
          return imageView;
      }
  
      @Override
      public boolean hasSubMenu(){
          return true;
      }
  
      @Override
      public void onPrepareSubMenu(SubMenu subMenu){
          subMenu.clear();
  
          subMenu.add("Sort by name").setOnMenuItemClickListener(this);
          subMenu.add("Sort by type").setOnMenuItemClickListener(this);
      }
  
      @Override
      public boolean onMenuItemClick(MenuItem item){
          Toast.makeText(mContext, "I was clicked!", Toast.LENGTH_SHORT).show();
          return true;
      }
  }
  </code></pre>
  
  <p>Menu:</p>
  
  <pre><code>&lt;menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:support="http://schemas.android.com/apk/res-auto" &gt;
  
      &lt;item
          android:id="@+id/menu_sort"
          android:actionProviderClass="com.myapp.provider.SortActionProvider"
          android:showAsAction="always"
          android:title="@string/sort"
          support:actionProviderClass="com.myapp.provider.SortActionProvider"
          support:showAsAction="always"/&gt;
  
  &lt;/menu&gt;
  </code></pre>