mus: Add EventObserver to allow passively listening to UI events

components/mus/ws/window_manager_state_unittest.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 "components/mus/ws/window_manager_state.h"
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/thread_task_runner_handle.h"
-#include "components/mus/public/cpp/event_matcher.h"
+#include "components/mus/public/cpp/event_matcher_util.h"
 #include "components/mus/surfaces/surfaces_state.h"
 #include "components/mus/ws/accelerator.h"
 #include "components/mus/ws/display_binding.h"
 #include "components/mus/ws/platform_display.h"
 #include "components/mus/ws/platform_display_init_params.h"
 #include "components/mus/ws/server_window_surface_manager_test_api.h"
 #include "components/mus/ws/test_change_tracker.h"
 #include "components/mus/ws/test_server_window_delegate.h"
 #include "components/mus/ws/test_utils.h"
 #include "components/mus/ws/window_manager_access_policy.h"
@@ skipping 325 matching lines @@
             ChangesToDescription1(*tracker->changes())[0]);
 
   OnEventAckTimeout();
   EXPECT_TRUE(window_manager()->on_accelerator_called());
   EXPECT_EQ(accelerator->id(), window_manager()->on_accelerator_id());
 }
 
 }  // namespace test
 }  // namespace ws
 }  // namespace mus