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

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 8cdfec9c861977a5c88ca323d51d7546de3f1125..665d81a94bd4bcc83096667eb8e6ad26e94d49ac 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -935,9 +935,8 @@ void Shell::Init(const ShellInitParams& init_params) {
   accelerator_controller_ = shell_port_->CreateAcceleratorController();
   maximize_mode_controller_ = base::MakeUnique<MaximizeModeController>();
 
-  if (config == Config::CLASSIC) {
-    // Not applicable to mus/mash as events are already routed to InputMethod
-    // first.
+  if (config == Config::CLASSIC || config == Config::MUS) {
+    // Not applicable to mash as events are already routed to InputMethod first.
     AddPreTargetHandler(
         window_tree_host_manager_->input_method_event_handler());
   }