StructTraits to map mus::mojom::Event to unique_ptr<ui::Event>

mash/app_driver/app_driver.cc

Index: mash/app_driver/app_driver.cc
diff --git a/mash/app_driver/app_driver.cc b/mash/app_driver/app_driver.cc
index a676c73b03a6cc1f38fbdfcd89ba98ae0e218409..bca1280df2f7160db955ece2978f57d306807450 100644
--- a/mash/app_driver/app_driver.cc
+++ b/mash/app_driver/app_driver.cc
@@ -102,7 +102,8 @@ bool AppDriver::ShellConnectionLost() {
   return true;
 }
 
-void AppDriver::OnAccelerator(uint32_t id, mus::mojom::EventPtr event) {
+void AppDriver::OnAccelerator(uint32_t id,
+                              const std::unique_ptr<ui::Event>& event) {
   struct LaunchOptions {
     uint32_t option;
     const char* app;