Makes WindowTree::SetFocus(null) work

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 145 matching lines @@
   void OnEmbedImpl(mojom::WindowTree* window_tree,
                    ConnectionSpecificId connection_id,
                    mojom::WindowDataPtr root_data,
                    Id focused_window_id);
 
   // Overridden from WindowTreeConnection:
   void SetDeleteOnNoRoots(bool value) override;
   const std::set<Window*>& GetRoots() override;
   Window* GetWindowById(Id id) override;
   Window* GetFocusedWindow() override;
+  void ClearFocus() override;
   Window* NewWindow(const Window::SharedProperties* properties) override;
   Window* NewTopLevelWindow(
       const Window::SharedProperties* properties) override;
   ConnectionSpecificId GetConnectionId() override;
   void AddObserver(WindowTreeConnectionObserver* observer) override;
   void RemoveObserver(WindowTreeConnectionObserver* observer) override;
 
   // Overridden from WindowTreeClient:
   void OnEmbed(ConnectionSpecificId connection_id,
                mojom::WindowDataPtr root,
@@ skipping 110 matching lines @@
   scoped_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_