mash: Port mojo:ash_sysui's ContextMenuMus to mojo:ash.

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 964a1dfeaa85851962ed4bc7231afc88b55bc18e..bbb2d647e609a9b1adc42e7462c93c3ce7c78a9c 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -15,6 +15,7 @@
 #include "ash/mus/bridge/wm_shell_mus.h"
 #include "ash/mus/bridge/wm_window_mus.h"
 #include "ash/mus/move_event_handler.h"
+#include "ash/mus/native_widget_factory_mus.h"
 #include "ash/mus/non_client_frame_controller.h"
 #include "ash/mus/property_util.h"
 #include "ash/mus/root_window_controller.h"
@@ -103,6 +104,8 @@ void WindowManager::Init(ui::WindowTreeClient* window_tree_client) {
                               pointer_watcher_event_router_.get()));
   shell_->Initialize();
   lookup_.reset(new WmLookupMus);
+
+  native_widget_factory_mus_.reset(new NativeWidgetFactoryMus(this));
 }
 
 void WindowManager::SetScreenLocked(bool is_locked) {
@@ -219,6 +222,8 @@ void WindowManager::OnDidDestroyClient(ui::WindowTreeClient* client) {
   FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
                     OnWindowTreeClientDestroyed());
 
+  native_widget_factory_mus_.reset();
+
   lookup_.reset();
   shell_->Shutdown();
   shell_.reset();