mash: make Env::last_mouse_location() accurate for Mus

ui/aura/test/aura_test_base.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/test/aura_test_base.h"
 
 #include "ui/aura/client/window_parenting_client.h"
 #include "ui/aura/mus/property_utils.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/mus/window_tree_host_mus.h"
@@ skipping 231 matching lines @@
   DCHECK(setup_called_);
 }
 
 void AuraTestBaseWithType::SetUp() {
   DCHECK(!setup_called_);
   setup_called_ = true;
   ConfigureBackend(GetParam());
   AuraTestBase::SetUp();
 }
 
+AuraTestBaseMus::AuraTestBaseMus() {}
+
+AuraTestBaseMus::~AuraTestBaseMus() {}
+
+void AuraTestBaseMus::SetUp() {
+  ConfigureBackend(test::BackendType::MUS);
+  AuraTestBase::SetUp();
+}
+
 }  // namespace test
 }  // namespace aura