Close IME Mojo service on disconneciton.

We should release the Utility process when the last client is gone.

Bug: 837156
Change-Id: I66dc753d45a43455dc8cd4a8e759436ec330624a
Reviewed-on: https://chromium-review.googlesource.com/c/1349159Reviewed-by: Shu Chen <shuchen@chromium.org>
Commit-Queue: Shu Chen <shuchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610552}

chromeos/services/ime/ime_service.cc

@@ -62,6 +62,7 @@ void ImeService::BindInputEngineManagerRequest(
 
 void ImeService::OnConnectionLost() {
   if (engine_manager_bindings_.empty()) {
+    service_binding_.RequestClose();
     // TODO(https://crbug.com/837156): Set a timer to start a cleanup.
   }
 }