aura-mus: Implement Deactivate().

ui/aura/mus/focus_synchronizer.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 "ui/aura/mus/focus_synchronizer.h"
 
 #include "base/auto_reset.h"
 #include "services/ui/public/interfaces/window_tree.mojom.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/env.h"
@@ skipping 28 matching lines @@
     // The client should provide a focus client for all roots.
     DCHECK(client::GetFocusClient(root));
     if (env->active_focus_client_root() != root)
       env->SetActiveFocusClient(client::GetFocusClient(root), root);
     window->GetWindow()->Focus();
   } else if (env->active_focus_client()) {
     env->active_focus_client()->FocusWindow(nullptr);
   }
 }
 
+void FocusSynchronizer::ClearFocus() {
+  SetFocusedWindow(nullptr);
+}
+
 void FocusSynchronizer::OnFocusedWindowDestroyed() {
   focused_window_ = nullptr;
 }
 
 void FocusSynchronizer::SetActiveFocusClient(
     client::FocusClient* focus_client) {
   if (focus_client == active_focus_client_)
     return;
 
   if (active_focus_client_)
@@ skipping 32 matching lines @@
   if (focus_client) {
     Window* focused_window = focus_client->GetFocusedWindow();
     SetFocusedWindow(focused_window ? WindowMus::Get(focused_window)
                                     : WindowMus::Get(window));
   } else {
     SetFocusedWindow(nullptr);
   }
 }
 
 }  // namespace aura