Adding a missing documentation of the ActionProvider ActionBar sample.

Change-Id: I09772305953f7684388603f3f34ec21c64a09067
diff --git a/samples/ApiDemos/src/com/example/android/apis/app/_index.html b/samples/ApiDemos/src/com/example/android/apis/app/_index.html
index 81d567d..4333d57 100644
--- a/samples/ApiDemos/src/com/example/android/apis/app/_index.html
+++ b/samples/ApiDemos/src/com/example/android/apis/app/_index.html
@@ -160,6 +160,10 @@
 default Honeycomb theme includes the Action Bar by default and a menu resource is used to populate
 the menu data itself. If you'd like to see how these things work under the hood, see
 Mechanics.</dd>
+  <dt><a href="ActionBarActionProviderActivity.html">ActionProvider</a></dt>
+  <dd>Shows how to use an ActionProvider to supply a menu item with a specialized action view and
+  handle standard menu item clicks in one place. Demonstrated using the streamlined sharing UI
+  added in ICS. </dd>
   <dt><a href="ActionBarDisplayOptions.html">Display Options</a></dt>
   <dd>Shows how various Action Bar display option flags can be combined and their effects.</dd>
 </dl>