[views-mus] Prevent creating a native OzonePlatform in mus tests.

ui/views/mus/views_mus_test_suite.cc

 // Copyright 2016 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/views/mus/views_mus_test_suite.h"
 
 #include <memory>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 243 matching lines @@
 
   ViewsTestSuite::Initialize();
   service_manager_connections_ = base::MakeUnique<ServiceManagerConnection>();
 }
 
 void ViewsMusTestSuite::Shutdown() {
   service_manager_connections_.reset();
   ViewsTestSuite::Shutdown();
 }
 
+void ViewsMusTestSuite::InitializeEnv() {
+  env_ = aura::Env::CreateInstance(aura::Env::Mode::MUS);
+}
+
+void ViewsMusTestSuite::DestroyEnv() {
+  env_.reset();
+}
+
 }  // namespace views