Emit 'execute' event when menu item is clicked.

browser/api/atom_api_menu.cc

@@ -106,6 +106,11 @@ string16 Menu::GetSublabelForCommandId(int command_id) const {
 }
 
 void Menu::ExecuteCommand(int command_id, int event_flags) {
+  v8::Handle<v8::Value> args[] = {
+    v8::String::New("execute"),
+    v8::Integer::New(command_id)
+  };
+  node::MakeCallback(handle(), "emit", 2, args);
 }
 
 // static