Change AckEvent into request / response

mojo/examples/sample_app/sample_app.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdio.h>
 #include <string>
 
 #include "mojo/examples/sample_app/gles2_client_impl.h"
 #include "mojo/public/bindings/allocation_scope.h"
 #include "mojo/public/bindings/remote_ptr.h"
@@ skipping 53 matching lines @@
   }
 
   virtual void OnDestroyed() MOJO_OVERRIDE {
     RunLoop::current()->Quit();
   }
 
   virtual void OnBoundsChanged(const Rect& bounds) MOJO_OVERRIDE {
     gles2_client_->SetSize(bounds.size());
   }
 
-  virtual void OnEvent(const Event& event) MOJO_OVERRIDE {
-    if (!event.location().is_null()) {
+  virtual void OnEvent(const Event& event,
+                       const mojo::Callback<void()>& callback) MOJO_OVERRIDE {
+    if (!event.location().is_null())
       gles2_client_->HandleInputEvent(event);
-      viewport_->AckEvent(event);
-    }
+    callback.Run();
   }
 
  private:
   scoped_ptr<GLES2ClientImpl> gles2_client_;
   RemotePtr<NativeViewport> viewport_;
 };
 
 }  // namespace examples
 }  // namespace mojo
 
 extern "C" SAMPLE_APP_EXPORT MojoResult CDECL MojoMain(
     MojoHandle shell_handle) {
   mojo::Environment env;
   mojo::RunLoop loop;
   mojo::GLES2Initializer gles2;
 
   mojo::examples::SampleApp app(shell_handle);
   loop.Run();
   return MOJO_RESULT_OK;
 }