aura-mus: Implement Deactivate().

ui/aura/mus/window_tree_host_mus.h

 // Copyright 2015 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 UI_AURA_MUS_WINDOW_TREE_HOST_MUS_H_
 #define UI_AURA_MUS_WINDOW_TREE_HOST_MUS_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 49 matching lines @@
 
   InputMethodMus* input_method() { return input_method_.get(); }
 
   // Sets the client area on the underlying mus window.
   void SetClientArea(const gfx::Insets& insets);
 
   // Sets the hit test mask on the underlying mus window. Pass base::nullopt to
   // clear.
   void SetHitTestMask(const base::Optional<gfx::Rect>& rect);
 
+  // Sends a focus change to the mus server with a null window.
+  void ClearFocus();
+
   // Intended only for WindowTreeClient to call.
   void set_display_id(int64_t id) { display_id_ = id; }
   int64_t display_id() const { return display_id_; }
   display::Display GetDisplay() const;
 
   // aura::WindowTreeHostPlatform:
   void ShowImpl() override;
   void HideImpl() override;
   void SetBoundsInPixels(const gfx::Rect& bounds) override;
   void DispatchEvent(ui::Event* event) override;
@@ skipping 10 matching lines @@
   bool in_set_bounds_from_server_ = false;
 
   std::unique_ptr<InputMethodMus> input_method_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostMus);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_HOST_MUS_H_