mus: Add EventObserver to allow passively listening to UI events

components/mus/ws/window_manager_state.h

 // 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.
 
 #ifndef COMPONENTS_MUS_WS_WINDOW_MANAGER_STATE_H_
 #define COMPONENTS_MUS_WS_WINDOW_MANAGER_STATE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 146 matching lines @@
   void OnAccelerator(uint32_t accelerator_id, const ui::Event& event) override;
   void SetFocusedWindowFromEventDispatcher(ServerWindow* window) override;
   ServerWindow* GetFocusedWindowForEventDispatcher() override;
   void SetNativeCapture() override;
   void ReleaseNativeCapture() override;
   void OnServerWindowCaptureLost(ServerWindow* window) override;
   void DispatchInputEventToWindow(ServerWindow* target,
                                   bool in_nonclient_area,
                                   const ui::Event& event,
                                   Accelerator* accelerator) override;
+  void OnEventTargetNotFound(const ui::Event& event) override;
 
   Display* display_;
   PlatformDisplay* platform_display_;
   // If this was created implicitly by a call
   // WindowTreeHostFactory::CreateWindowTreeHost(), then |is_user_id_valid_|
   // is false.
   const bool is_user_id_valid_;
   const UserId user_id_;
   // Root ServerWindow of this WindowManagerState. |root_| has a parent, the
   // root ServerWindow of the Display.
@@ skipping 12 matching lines @@
 
   EventDispatcher event_dispatcher_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowManagerState);
 };
 
 }  // namespace ws
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_WS_WINDOW_MANAGER_STATE_H_