chromeos: fix focus for mushrome

ash/test/ash_test_helper.h

Index: ash/test/ash_test_helper.h
diff --git a/ash/test/ash_test_helper.h b/ash/test/ash_test_helper.h
index a53021f2375fada6b60f902f6fa0e0eaa22099a9..2aac0792f7960ec7c06a40b98d71454eb5437a41 100644
--- a/ash/test/ash_test_helper.h
+++ b/ash/test/ash_test_helper.h
@@ -109,6 +109,9 @@ class AshTestHelper {
   mus::WindowManagerApplication* window_manager_app() {
     return window_manager_app_.get();
   }
+  aura::TestWindowTreeClientSetup* window_tree_client_setup() {
+    return &window_tree_client_setup_;
+  }
 
   TestSessionControllerClient* test_session_controller_client() {
     return session_controller_client_.get();