aura-mus: Implement Deactivate().

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 589769b77be289e2ff70360d39c28678c16acf53..262cfead74bc90d3a1743524dc4094c428eed478 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -507,5 +507,13 @@ void WindowManager::OnWmSetClientArea(
   non_client_frame_controller->SetClientArea(insets, additional_client_areas);
 }
 
+bool WindowManager::IsWindowActive(aura::Window* window) {
+  return activation_client()->GetActiveWindow() == window;
+}
+
+void WindowManager::OnWmDeactivateWindow(aura::Window* window) {
+  activation_client()->DeactivateWindow(window);
+}
+
 }  // namespace mus
 }  // namespace ash