mus: Add EventObserver to allow passively listening to UI events

components/mus/public/cpp/lib/window_tree_client_impl.h

 // Copyright 2014 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_PUBLIC_CPP_LIB_WINDOW_TREE_CLIENT_IMPL_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_LIB_WINDOW_TREE_CLIENT_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 202 matching lines @@
   void OnWindowVisibilityChanged(Id window_id, bool visible) override;
   void OnWindowOpacityChanged(Id window_id,
                               float old_opacity,
                               float new_opacity) override;
   void OnWindowParentDrawnStateChanged(Id window_id, bool drawn) override;
   void OnWindowSharedPropertyChanged(Id window_id,
                                      const mojo::String& name,
                                      mojo::Array<uint8_t> new_data) override;
   void OnWindowInputEvent(uint32_t event_id,
                           Id window_id,
-                          mojom::EventPtr event) override;
+                          mojom::EventPtr event,
+                          uint32_t event_observer_id) override;
+  void OnEventObserved(mojom::EventPtr event,
+                       uint32_t event_observer_id) override;
   void OnWindowFocused(Id focused_window_id) override;
   void OnWindowPredefinedCursorChanged(Id window_id,
                                        mojom::Cursor cursor) override;
   void OnChangeCompleted(uint32_t change_id, bool success) override;
   void RequestClose(uint32_t window_id) override;
   void GetWindowManager(
       mojo::AssociatedInterfaceRequest<WindowManager> internal) override;
 
   // Overridden from WindowManager:
   void WmSetBounds(uint32_t change_id,
@@ skipping 61 matching lines @@
   std::unique_ptr<mojo::AssociatedBinding<mojom::WindowManager>>
       window_manager_internal_;
   mojom::WindowManagerClientAssociatedPtr window_manager_internal_client_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClientImpl);
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_LIB_WINDOW_TREE_CLIENT_IMPL_H_