Change AckEvent into request / response

mojo/examples/pepper_container_app/pepper_container_app.cc

Index: mojo/examples/pepper_container_app/pepper_container_app.cc
diff --git a/mojo/examples/pepper_container_app/pepper_container_app.cc b/mojo/examples/pepper_container_app/pepper_container_app.cc
index ec45a45c96b6ba9ad4aa0d409d501df740481966..44b3448fe5667e4004bf2c9ef80a7d40b8db176a 100644
--- a/mojo/examples/pepper_container_app/pepper_container_app.cc
+++ b/mojo/examples/pepper_container_app/pepper_container_app.cc
@@ -90,16 +90,14 @@ class PepperContainerApp: public Application,
       plugin_instance_->DidChangeView(bounds);
   }
 
-  virtual void OnEvent(const Event& event) OVERRIDE {
-    if (event.location().is_null())
-      return;
-
-    {
+  virtual void OnEvent(const Event& event,
+                       const mojo::Callback<void()>& callback) OVERRIDE {
+    if (!event.location().is_null()) {
       ppapi::ProxyAutoLock lock;
 
       // TODO(yzshen): Handle events.
     }
-    viewport_->AckEvent(event);
+    callback.Run();
   }
 
   // MojoPpapiGlobals::Delegate implementation.