Enable Config::MUS to use classic IME instead of servicified IME.

ui/aura/mus/window_tree_client.cc

Index: ui/aura/mus/window_tree_client.cc
diff --git a/ui/aura/mus/window_tree_client.cc b/ui/aura/mus/window_tree_client.cc
index 6f5956f9f4bae396b86542f3f28ea016abbcb7b1..3c87da5b008e9222b73f692e0f0f44896af9a99a 100644
--- a/ui/aura/mus/window_tree_client.cc
+++ b/ui/aura/mus/window_tree_client.cc
@@ -184,6 +184,12 @@ void DispatchEventToTarget(ui::Event* event, WindowMus* target) {
   GetWindowTreeHostMus(target)->SendEventToSink(event);
 }
 
+void IMEAckCallback(std::unique_ptr<EventResultCallback> result_callback,
+                    bool handled) {
+  result_callback->Run(handled ? ui::mojom::EventResult::HANDLED
+                               : ui::mojom::EventResult::UNHANDLED);
+}
+
 }  // namespace
 
 WindowTreeClient::WindowTreeClient(
@@ -1235,9 +1241,10 @@ void WindowTreeClient::OnWindowInputEvent(uint32_t event_id,
       tree_->OnWindowInputEventAck(event_id, ui::mojom::EventResult::UNHANDLED);
       return;
     }
-    InputMethodMus* input_method = GetWindowTreeHostMus(window)->input_method();
-    input_method->DispatchKeyEvent(event->AsKeyEvent(),
-                                   CreateEventResultCallback(event_id));
+    GetWindowTreeHostMus(window)->DispatchEventToInputMethod(
+        event->AsKeyEvent(),
+        base::MakeUnique<InputMethodMus::AckCallback>(base::Bind(
+            &IMEAckCallback, Passed(CreateEventResultCallback(event_id)))));
     return;
   }